expertenaustausch > comp.lang.* > comp.lang.c

Thomas Koenig (03.06.2020, 18:54)
Auf modernen 64-Bit-Systemen mit virtuellem Speicher funktioniert
normalerweise jedes malloc() und liefert einen Pointer auf einen
Speicherbereich zurück. Wenn man den Speicher dann wirklich
verwenden möchte und der dann dank memory overcommitment dann doch
nicht wirklich da ist, wundert man sich über ein einfrierendes
System, einen Absturz oder dass irgendwas anderes abgeschossen
wird...

Gibt es da eigentlich Implementierungen von malloc, denen man eine
Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?

Sowas könnte für embedded Systeme interessant sein (falls man da
überhaupt malloc verwenden sollte), aber auch moderne Supercomputer
haben mittlerweile viele CPUs, aber die GB pro Core gehen eher
runter.

Selber müsste man sich für sowas vermutlich einen Wrapper
schreiben.
Bonita Montero (03.06.2020, 21:11)
> Auf modernen 64-Bit-Systemen mit virtuellem Speicher funktioniert
> normalerweise jedes malloc() und liefert einen Pointer auf einen
> Speicherbereich zurück. Wenn man den Speicher dann wirklich
> verwenden möchte und der dann dank memory overcommitment dann doch
> nicht wirklich da ist, wundert man sich über ein einfrierendes
> System, einen Absturz oder dass irgendwas anderes abgeschossen
> wird...
> Gibt es da eigentlich Implementierungen von malloc, denen man eine
> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?


Hilft dir ja nicht bei deinem Problem, dass Overcommit unzuverlässig
ist.

> Selber müsste man sich für sowas vermutlich einen Wrapper
> schreiben.


Schwieriger wirds wenn Du malloc selbst substituieren willst, dass
fremder Code deine Implementation nutzt.
Christian Weisgerber (03.06.2020, 21:26)
On 2020-06-03, Thomas Koenig <tkoenig> wrote:

> Gibt es da eigentlich Implementierungen von malloc, denen man eine
> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?


Auf OpenBSD begrenzt RLIMIT_DATA auch wirkungsvoll malloc(3).
Das ist aber nicht in malloc(3) implementiert, sondern mmap(2)
stellt sich schon quer.

Anderswo gibt es RLIMIT_AS.
Helmut Schellong (04.06.2020, 10:41)
On 06/03/2020 18:54, Thomas Koenig wrote:
> Auf modernen 64-Bit-Systemen mit virtuellem Speicher funktioniert
> normalerweise jedes malloc() und liefert einen Pointer auf einen
> Speicherbereich zurück. Wenn man den Speicher dann wirklich
> verwenden möchte und der dann dank memory overcommitment dann doch
> nicht wirklich da ist, wundert man sich über ein einfrierendes
> System, einen Absturz oder dass irgendwas anderes abgeschossen
> wird...
> Gibt es da eigentlich Implementierungen von malloc, denen man eine
> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?


FreeBSD
-------
Non-standard API
void *mallocx(size_t size, int flags);

void *rallocx(void *ptr, size_t size, int flags);

size_t xallocx(void *ptr, size_t size, size_t extra, int flags);

size_t sallocx(void *ptr, int flags);

void dallocx(void *ptr, int flags);

void sdallocx(void *ptr, size_t size, int flags);

size_t nallocx(size_t size, int flags);

int mallctl(const char *name, void *oldp, size_t *oldlenp, void *newp,
size_t newlen);

int mallctlnametomib(const char *name, size_t *mibp, size_t *miblenp);

int mallctlbymib(const size_t *mib, size_t miblen, void *oldp,
size_t *oldlenp, void *newp, size_t newlen);

void malloc_stats_print(void (*write_cb) (void *, const char *),
void *cbopaque, const char *opts);

size_t malloc_usable_size(const void *ptr);

void (*malloc_message)(void *cbopaque, const char *s);

const char *malloc_conf;
Thomas Koenig (04.06.2020, 14:11)
Helmut Schellong <rip> schrieb:
> On 06/03/2020 18:54, Thomas Koenig wrote:
> FreeBSD
> -------
> Non-standard API
> void *mallocx(size_t size, int flags);


Ohne Erklärung, was das jeweils tut, ist dein Artikel relativ
inhaltslos.
Thomas Koenig (04.06.2020, 14:12)
Christian Weisgerber <naddy> schrieb:
> On 2020-06-03, Thomas Koenig <tkoenig> wrote:
> Auf OpenBSD begrenzt RLIMIT_DATA auch wirkungsvoll malloc(3).
> Das ist aber nicht in malloc(3) implementiert, sondern mmap(2)
> stellt sich schon quer.
> Anderswo gibt es RLIMIT_AS.


Darüber kann man das natürlich auch machen, stimmt (man hat dann
zwar den ganzen Speicherbereich und nicht nur den dynamisch
allokierten, aber das kann ja je nach Aufgabenstellung sogar
sinnvoller sein). Danke!
Helmut Schellong (04.06.2020, 14:57)
On 06/04/2020 14:11, Thomas Koenig wrote:
> Helmut Schellong <rip> schrieb:
> Ohne Erklärung, was das jeweils tut, ist dein Artikel relativ
> inhaltslos.


401] u
total 32872
drwxrwxr-x 2 root operator 512 Feb 14 2014 .snap
-r-------- 1 root wheel 33554432 Sep 4 2017 .sujournal
drwx------ 4 root wheel 512 Feb 22 23:41 .Trash-0
drwx------ 3 root wheel 2048 Jan 9 2019 bin
drwxr-xr-x 16 root wheel 512 Jan 27 2019 bsh
drwx------ 4 root wheel 512 May 11 12:09 cie
drwx------ 11 root wheel 512 Dec 9 02:30 eagle
drwx------ 67 root wheel 1536 Apr 5 23:14 helmut
drwx------ 9 root wheel 1024 Apr 25 21:47 hp
drwx------ 19 root wheel 512 Apr 24 21:54 hs
drwx------ 14 root wheel 512 Apr 30 2006 l
drwxr-xr-x 2 root wheel 512 May 24 2018 links
drwx------ 10 root wheel 512 May 24 2015 sc
drwx------ 9 root wheel 512 Sep 12 2018 sh
drwxr-xr-x 3 root wheel 512 Jul 20 2011 svn
drwx------ 3 root wheel 1024 May 12 16:51 tmp
drwx------ 5 root wheel 512 Apr 23 19:48 wapi
drwx------ 2 root wheel 1024 Oct 6 2018 wiki
drwx------ 3 root wheel 512 Nov 9 2005 wir
/u : /dev/pts/0
402] pop.bish
/tmp/bish_tmpf.500
__________________________________________________ ________________________________________
194.25.134.110:995 securepop.t-online.de:995 schellong
'einDSacl1' n=? b=? t=? q=1
Info-Liste holen : i | I
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Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
H 3
__________________________________________________ ________________________________________
212.227.15.188 pop.ionos.de vs 'IOeimd#2sacl19' n=? b=?
t=? q=1
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Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
i

1 46262 H =?utf-8?Q?Wir_haben_Neuigkeiten_f=C ING
<noreply>
__________________________________________________ ________________________________________
212.227.15.188 pop.ionos.de vs 'IOeimd#2sacl19' n=1
b=46262 t=3628 q=1
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Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
H 2
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=1
b=46262 t=3628 q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
i

1 154164 M =?UTF-8?Q?Big_Tech:_Gewinner_der_Pa "Handelsblatt Morning
Briefing - C
2 37815 H 4.000 Punkte warten auf dich, liebe DeutschlandCard
<info
3 35013 M Sie haben eine private Nachricht in Telekom hilft
Community <noreply@c
4 34079 M =?UTF-8?Q?Eine_Antwort_auf_eine_von Telekom hilft
Community <noreply@c
5 208080 M Der Wumms-Abend von Berlin "Handelsblatt Morning
Briefing" <M
6 25532 M Ihre Meinung ist uns wichtig "Shell"
<clubsmart_de>
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=6
b=494683 t=23243 q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
h 1 5
read() 100
+OK POP server ready H mieue052 1N32AX-1ixovx28OD-0128QT
USER var
+OK password required for user "var"
PASS IOeimd#1sacl19
+OK mailbox "var" has 6 messages (494683 octets) H mieue052
STAT
+OK 6 494683
UIDL
+OK
1 1MhUcX-1j1tcJ3xa7-00eZEV
2 1MbA5u-1j9MhC1pBQ-00bQEI
DELE 2
+OK
3 1Mn1ur-1jE6J444BD-00k72a
DELE 3
+OK
4 1MMnfW-1jQ9ks2LCO-00ImnO
DELE 4
+OK
5 1Mmjw0-1jI3Iu2PLy-00jq0b
6 1MziWf-1ilkg20sWv-00vgpJ
DELE 6
+OK
QUIT
+OK POP server signing off
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=? b=?
t=? q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
E
403] man malloc
JEMALLOC(3) User Manual JEMALLOC(3)

NAME
jemalloc - general purpose memory allocation functions

LIBRARY
This manual describes jemalloc
4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can
be found at the jemalloc website[1].

The following configuration options are enabled in libc's built-in
jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap,
--enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and
--enable-xmalloc. Additionally, --enable-debug is enabled in
development versions of FreeBSD (controlled by the MALLOC_PRODUCTION
make variable).

SYNOPSIS
#include <stdlib.h>
#include <malloc_np.h>

Standard API
void *malloc(size_t size);

void *calloc(size_t number, size_t size);

int posix_memalign(void **ptr, size_t alignment, size_t size);

void *aligned_alloc(size_t alignment, size_t size);

void *realloc(void *ptr, size_t size);

void free(void *ptr);

Non-standard API
void *mallocx(size_t size, int flags);

void *rallocx(void *ptr, size_t size, int flags);

size_t xallocx(void *ptr, size_t size, size_t extra, int flags);

size_t sallocx(void *ptr, int flags);

void dallocx(void *ptr, int flags);

void sdallocx(void *ptr, size_t size, int flags);

size_t nallocx(size_t size, int flags);

int mallctl(const char *name, void *oldp, size_t *oldlenp, void *newp,
size_t newlen);

int mallctlnametomib(const char *name, size_t *mibp, size_t *miblenp);

int mallctlbymib(const size_t *mib, size_t miblen, void *oldp,
size_t *oldlenp, void *newp, size_t newlen);

void malloc_stats_print(void (*write_cb) (void *, const char *),
void *cbopaque, const char *opts);

size_t malloc_usable_size(const void *ptr);

void (*malloc_message)(void *cbopaque, const char *s);

const char *malloc_conf;

DESCRIPTION
Standard API
404] ti
273+37
310
273+17
290
d=pow(310,4)-pow(290,4)
2162400000.000000012
0.5*5e-8*d*(1500/10000)
8.109000000000000046

405] cd hp/de/img/div
total 648
-rw-r--r-- 1 root wheel 32573 May 16 19:21 alulot.jpg
-rw-r--r-- 1 root wheel 35824 Jun 4 11:46
anschlussblock_fussbodenheizung.jpg
-rw-r--r-- 1 root wheel 336885 Jun 3 16:37 fbheiz.jpg
-rw-r--r-- 1 root wheel 250435 May 31 11:35 led1521lm12,5W.jpg
/u/hp/de/img/div : /dev/pts/0
406] mv ans* fbheiz2.jpg
407] l
total 648
-rw-r--r-- 1 root wheel 32573 May 16 19:21 alulot.jpg
-rw-r--r-- 1 root wheel 336885 Jun 3 16:37 fbheiz.jpg
-rw-r--r-- 1 root wheel 35824 Jun 4 11:46 fbheiz2.jpg
-rw-r--r-- 1 root wheel 250435 May 31 11:35 led1521lm12,5W.jpg
408] sftp 1u1
Connected to 1u1.
sftp> cd de/img/div
sftp> ls -l
-rw----r-- 1 2469023 600 32573 May 16 19:36 alulot.jpg
-rw----r-- 1 2469023 600 336885 Jun 3 16:39 fbheiz.jpg
-rw----r-- 1 2469023 600 250435 May 31 11:37 led1521lm12,5W.jpg
sftp> put fbheiz2.jpg
Uploading fbheiz2.jpg to /de/img/div/fbheiz2.jpg
fbheiz2.jpg 100%
35KB 436.6KB/s 00:00
sftp> ls -l
-rw----r-- 1 2469023 600 32573 May 16 19:36 alulot.jpg
-rw----r-- 1 2469023 600 336885 Jun 3 16:39 fbheiz.jpg
-rw----r-- 1 2469023 600 35824 Jun 4 11:53 fbheiz2.jpg
-rw----r-- 1 2469023 600 250435 May 31 11:37 led1521lm12,5W.jpg
sftp> quit
409] spch
410] man malloc
JEMALLOC(3) User Manual JEMALLOC(3)

NAME
jemalloc - general purpose memory allocation functions

LIBRARY
This manual describes jemalloc
4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can
be found at the jemalloc website[1].

The following configuration options are enabled in libc's built-in
jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap,
--enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and
--enable-xmalloc. Additionally, --enable-debug is enabled in
development versions of FreeBSD (controlled by the MALLOC_PRODUCTION
make variable).

SYNOPSIS
#include <stdlib.h>
#include <malloc_np.h>

Standard API
void *malloc(size_t size);

void *calloc(size_t number, size_t size);

int posix_memalign(void **ptr, size_t alignment, size_t size);

void *aligned_alloc(size_t alignment, size_t size);

void *realloc(void *ptr, size_t size);

void free(void *ptr);
401] u
total 32872
drwxrwxr-x 2 root operator 512 Feb 14 2014 .snap
-r-------- 1 root wheel 33554432 Sep 4 2017 .sujournal
drwx------ 4 root wheel 512 Feb 22 23:41 .Trash-0
drwx------ 3 root wheel 2048 Jan 9 2019 bin
drwxr-xr-x 16 root wheel 512 Jan 27 2019 bsh
drwx------ 4 root wheel 512 May 11 12:09 cie
drwx------ 11 root wheel 512 Dec 9 02:30 eagle
drwx------ 67 root wheel 1536 Apr 5 23:14 helmut
drwx------ 9 root wheel 1024 Apr 25 21:47 hp
drwx------ 19 root wheel 512 Apr 24 21:54 hs
drwx------ 14 root wheel 512 Apr 30 2006 l
drwxr-xr-x 2 root wheel 512 May 24 2018 links
drwx------ 10 root wheel 512 May 24 2015 sc
drwx------ 9 root wheel 512 Sep 12 2018 sh
drwxr-xr-x 3 root wheel 512 Jul 20 2011 svn
drwx------ 3 root wheel 1024 May 12 16:51 tmp
drwx------ 5 root wheel 512 Apr 23 19:48 wapi
drwx------ 2 root wheel 1024 Oct 6 2018 wiki
drwx------ 3 root wheel 512 Nov 9 2005 wir
/u : /dev/pts/0
402] pop.bish
/tmp/bish_tmpf.500
__________________________________________________ ________________________________________
194.25.134.110:995 securepop.t-online.de:995 schellong
'einDSacl1' n=? b=? t=? q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
H 3
__________________________________________________ ________________________________________
212.227.15.188 pop.ionos.de vs 'IOeimd#2sacl19' n=? b=?
t=? q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
i

1 46262 H =?utf-8?Q?Wir_haben_Neuigkeiten_f=C ING
<noreply>
__________________________________________________ ________________________________________
212.227.15.188 pop.ionos.de vs 'IOeimd#2sacl19' n=1
b=46262 t=3628 q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
H 2
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=1
b=46262 t=3628 q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
i

1 154164 M =?UTF-8?Q?Big_Tech:_Gewinner_der_Pa "Handelsblatt Morning
Briefing - C
2 37815 H 4.000 Punkte warten auf dich, liebe DeutschlandCard
<info
3 35013 M Sie haben eine private Nachricht in Telekom hilft
Community <noreply@c
4 34079 M =?UTF-8?Q?Eine_Antwort_auf_eine_von Telekom hilft
Community <noreply@c
5 208080 M Der Wumms-Abend von Berlin "Handelsblatt Morning
Briefing" <M
6 25532 M Ihre Meinung ist uns wichtig "Shell"
<clubsmart_de>
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=6
b=494683 t=23243 q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
h 1 5
read() 100
+OK POP server ready H mieue052 1N32AX-1ixovx28OD-0128QT
USER var
+OK password required for user "var"
PASS IOeimd#1sacl19
+OK mailbox "var" has 6 messages (494683 octets) H mieue052
STAT
+OK 6 494683
UIDL
+OK
1 1MhUcX-1j1tcJ3xa7-00eZEV
2 1MbA5u-1j9MhC1pBQ-00bQEI
DELE 2
+OK
3 1Mn1ur-1jE6J444BD-00k72a
DELE 3
+OK
4 1MMnfW-1jQ9ks2LCO-00ImnO
DELE 4
+OK
5 1Mmjw0-1jI3Iu2PLy-00jq0b
6 1MziWf-1ilkg20sWv-00vgpJ
DELE 6
+OK
QUIT
+OK POP server signing off
__________________________________________________ ________________________________________
212.227.15.171 pop.ionos.de var 'IOeimd#1sacl19' n=? b=?
t=? q=1
Info-Liste holen : i | I
Loeschen : l {n|v-b}... | * | tHM- | {min.max|min.|.max}
Halten : h {n|v-b}... | tHM- | {min.max|min.|.max}
Beenden : E
E
403] man malloc
JEMALLOC(3) User Manual JEMALLOC(3)

NAME
jemalloc - general purpose memory allocation functions

LIBRARY
This manual describes jemalloc
4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can
be found at the jemalloc website[1].

The following configuration options are enabled in libc's built-in
jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap,
--enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and
--enable-xmalloc. Additionally, --enable-debug is enabled in
development versions of FreeBSD (controlled by the MALLOC_PRODUCTION
make variable).

SYNOPSIS
#include <stdlib.h>
#include <malloc_np.h>

Standard API
void *malloc(size_t size);

void *calloc(size_t number, size_t size);

int posix_memalign(void **ptr, size_t alignment, size_t size);

void *aligned_alloc(size_t alignment, size_t size);

void *realloc(void *ptr, size_t size);

void free(void *ptr);

Non-standard API
void *mallocx(size_t size, int flags);

void *rallocx(void *ptr, size_t size, int flags);

size_t xallocx(void *ptr, size_t size, size_t extra, int flags);

size_t sallocx(void *ptr, int flags);

void dallocx(void *ptr, int flags);

void sdallocx(void *ptr, size_t size, int flags);

size_t nallocx(size_t size, int flags);

int mallctl(const char *name, void *oldp, size_t *oldlenp, void *newp,
size_t newlen);

int mallctlnametomib(const char *name, size_t *mibp, size_t *miblenp);

int mallctlbymib(const size_t *mib, size_t miblen, void *oldp,
size_t *oldlenp, void *newp, size_t newlen);

void malloc_stats_print(void (*write_cb) (void *, const char *),
void *cbopaque, const char *opts);

size_t malloc_usable_size(const void *ptr);

void (*malloc_message)(void *cbopaque, const char *s);

const char *malloc_conf;

DESCRIPTION
Standard API
404] ti
273+37
310
273+17
290
d=pow(310,4)-pow(290,4)
2162400000.000000012
0.5*5e-8*d*(1500/10000)
8.109000000000000046

405] cd hp/de/img/div
total 648
-rw-r--r-- 1 root wheel 32573 May 16 19:21 alulot.jpg
-rw-r--r-- 1 root wheel 35824 Jun 4 11:46
anschlussblock_fussbodenheizung.jpg
-rw-r--r-- 1 root wheel 336885 Jun 3 16:37 fbheiz.jpg
-rw-r--r-- 1 root wheel 250435 May 31 11:35 led1521lm12,5W.jpg
/u/hp/de/img/div : /dev/pts/0
406] mv ans* fbheiz2.jpg
407] l
total 648
-rw-r--r-- 1 root wheel 32573 May 16 19:21 alulot.jpg
-rw-r--r-- 1 root wheel 336885 Jun 3 16:37 fbheiz.jpg
-rw-r--r-- 1 root wheel 35824 Jun 4 11:46 fbheiz2.jpg
-rw-r--r-- 1 root wheel 250435 May 31 11:35 led1521lm12,5W.jpg
408] sftp 1u1
Connected to 1u1.
sftp> cd de/img/div
sftp> ls -l
-rw----r-- 1 2469023 600 32573 May 16 19:36 alulot.jpg
-rw----r-- 1 2469023 600 336885 Jun 3 16:39 fbheiz.jpg
-rw----r-- 1 2469023 600 250435 May 31 11:37 led1521lm12,5W.jpg
sftp> put fbheiz2.jpg
Uploading fbheiz2.jpg to /de/img/div/fbheiz2.jpg
fbheiz2.jpg 100%
35KB 436.6KB/s 00:00
sftp> ls -l
-rw----r-- 1 2469023 600 32573 May 16 19:36 alulot.jpg
-rw----r-- 1 2469023 600 336885 Jun 3 16:39 fbheiz.jpg
-rw----r-- 1 2469023 600 35824 Jun 4 11:53 fbheiz2.jpg
-rw----r-- 1 2469023 600 250435 May 31 11:37 led1521lm12,5W.jpg
sftp> quit
409] spch
410] man malloc
JEMALLOC(3) User Manual JEMALLOC(3)

NAME
jemalloc - general purpose memory allocation functions

LIBRARY
This manual describes jemalloc
4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can
be found at the jemalloc website[1].

The following configuration options are enabled in libc's built-in
jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap,
--enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and
--enable-xmalloc. Additionally, --enable-debug is enabled in
development versions of FreeBSD (controlled by the MALLOC_PRODUCTION
make variable).

SYNOPSIS
#include <stdlib.h>
#include <malloc_np.h>

Standard API
void *malloc(size_t size);

void *calloc(size_t number, size_t size);

int posix_memalign(void **ptr, size_t alignment, size_t size);

void *aligned_alloc(size_t alignment, size_t size);

void *realloc(void *ptr, size_t size);

void free(void *ptr);
411] man malloc | gvim -
Vim: Reading from stdin...
412] man malloc
JEMALLOC(3) User Manual JEMALLOC(3)

NAME
jemalloc - general purpose memory allocation functions

LIBRARY
This manual describes jemalloc
4.2.1-0-g3de035335255d553bdb344c32ffdb603816195d8. More information can
be found at the jemalloc website[1].

The following configuration options are enabled in libc's built-in
jemalloc: --enable-fill, --enable-lazy-lock, --enable-munmap,
--enable-stats, --enable-tcache, --enable-tls, --enable-utrace, and
--enable-xmalloc. Additionally, --enable-debug is enabled in
development versions of FreeBSD (controlled by the MALLOC_PRODUCTION
make variable).

SYNOPSIS
#include <stdlib.h>
#include <malloc_np.h>

Standard API
void *malloc(size_t size);

void *calloc(size_t number, size_t size);

int posix_memalign(void **ptr, size_t alignment, size_t size);

void *aligned_alloc(size_t alignment, size_t size);

void *realloc(void *ptr, size_t size);

void free(void *ptr);

Non-standard API
void *mallocx(size_t size, int flags);

void *rallocx(void *ptr, size_t size, int flags);

size_t xallocx(void *ptr, size_t size, size_t extra, int flags);

size_t sallocx(void *ptr, int flags);

void dallocx(void *ptr, int flags);

void sdallocx(void *ptr, size_t size, int flags);

size_t nallocx(size_t size, int flags);

int mallctl(const char *name, void *oldp, size_t *oldlenp, void *newp,
size_t newlen);

int mallctlnametomib(const char *name, size_t *mibp, size_t *miblenp);

int mallctlbymib(const size_t *mib, size_t miblen, void *oldp,
size_t *oldlenp, void *newp, size_t newlen);

void malloc_stats_print(void (*write_cb) (void *, const char *),
void *cbopaque, const char *opts);

size_t malloc_usable_size(const void *ptr);

void (*malloc_message)(void *cbopaque, const char *s);

const char *malloc_conf;

DESCRIPTION
Standard API

Non-standard API
The mallocx, rallocx, xallocx, sallocx, dallocx, sdallocx, and nallocx
functions all have a flags argument that can be used to specify
options. The functions only check the options that are contextually
relevant. Use bitwise or (|) operations to specify one or more of the
following:

MALLOCX_LG_ALIGN(la)
Align the memory allocation to start at an address that is a
multiple of (1 << la). This macro does not validate that la is
within the valid range.

MALLOCX_ALIGN(a)
Align the memory allocation to start at an address that is a
multiple of a, where a is a power of two. This macro does not
validate that a is a power of 2.

MALLOCX_ZERO
Initialize newly allocated memory to contain zero bytes. In the
growing reallocation case, the real size prior to reallocation
defines the boundary between untouched bytes and those that are
initialized to contain zero bytes. If this macro is absent, newly
allocated memory is uninitialized.

MALLOCX_TCACHE(tc)
Use the thread-specific cache (tcache) specified by the identifier
tc, which must have been acquired via the "tcache.create" mallctl.
This macro does not validate that tc specifies a valid identifier.

MALLOCX_TCACHE_NONE
Do not use a thread-specific cache (tcache). Unless
MALLOCX_TCACHE(tc) or MALLOCX_TCACHE_NONE is specified, an
automatically managed tcache will be used under many circumstances.
This macro cannot be used in the same flags argument as
MALLOCX_TCACHE(tc).

MALLOCX_ARENA(a)
Use the arena specified by the index a. This macro has no effect
for regions that were allocated via an arena other than the one
specified. This macro does not validate that a specifies an arena
index in the valid range.

The mallocx function allocates at least size bytes of memory, and
returns a pointer to the base address of the allocation. Behavior is
undefined if size is 0.

The rallocx function resizes the allocation at ptr to be at least size
bytes, and returns a pointer to the base address of the resulting
allocation, which may or may not have moved from its original location.
Behavior is undefined if size is 0.

The xallocx function resizes the allocation at ptr in place to be at
least size bytes, and returns the real size of the allocation. If extra
is non-zero, an attempt is made to resize the allocation to be at least
(size + extra) bytes, though inability to allocate the extra byte(s)
will not by itself result in failure to resize. Behavior is undefined
if size is 0, or if (size + extra > SIZE_T_MAX).

The sallocx function returns the real size of the allocation at ptr.

The dallocx function causes the memory referenced by ptr to be made
available for future allocations.

The sdallocx function is an extension of dallocx with a size parameter
to allow the caller to pass in the allocation size as an optimization.
The minimum valid input size is the original requested size of the
allocation, and the maximum valid input size is the corresponding value
returned by nallocx or sallocx.
The nallocx function allocates no memory, but it performs the same size
computation as the mallocx function, and returns the real size of the
allocation that would result from the equivalent mallocx function call,
or 0 if the inputs exceed the maximum supported size class and/or
alignment. Behavior is undefined if size is 0.

The mallctl function provides a general interface for introspecting the
memory allocator, as well as setting modifiable parameters and
triggering actions. The period-separated name argument specifies a
location in a tree-structured namespace; see the MALLCTL NAMESPACE
section for documentation on the tree contents. To read a value, pass a
pointer via oldp to adequate space to contain the value, and a pointer
to its length via oldlenp; otherwise pass NULL and NULL. Similarly, to
write a value, pass a pointer to the value via newp, and its length via
newlen; otherwise pass NULL and 0.

The mallctlnametomib function provides a way to avoid repeated name
lookups for applications that repeatedly query the same portion of the
namespace, by translating a name to a "Management Information Base"
(MIB) that can be passed repeatedly to mallctlbymib. Upon successful
return from mallctlnametomib, mibp contains an array of *miblenp
integers, where *miblenp is the lesser of the number of components in
name and the input value of *miblenp. Thus it is possible to pass a
*miblenp that is smaller than the number of period-separated name
components, which results in a partial MIB that can be used as the
basis for constructing a complete MIB. For name components that are
integers (e.g. the 2 in "arenas.bin.2.size"), the corresponding MIB
component will always be that integer. Therefore, it is legitimate to
construct code like the following:

unsigned nbins, i;
size_t mib[4];
size_t len, miblen;

len = sizeof(nbins);
mallctl("arenas.nbins", &nbins, &len, NULL, 0);

miblen = 4;
mallctlnametomib("arenas.bin.0.size", mib, &miblen);
for (i = 0; i < nbins; i++) {
size_t bin_size;

mib[2] = i;
len = sizeof(bin_size);
mallctlbymib(mib, miblen, &bin_size, &len, NULL, 0);
/* Do something with bin_size... */
}

The malloc_stats_print function writes human-readable summary
statistics via the write_cb callback function pointer and cbopaque data
passed to write_cb, or malloc_message if write_cb is NULL. This
function can be called repeatedly. General information that never
changes during execution can be omitted by specifying "g" as a
character within the opts string. Note that malloc_message uses the
mallctl* functions internally, so inconsistent statistics can be
reported if multiple threads use these functions simultaneously. If
--enable-stats is specified during configuration, "m" and "a" can be
specified to omit merged arena and per arena statistics, respectively;
"b", "l", and "h" can be specified to omit per size class statistics
for bins, large objects, and huge objects, respectively. Unrecognized
characters are silently ignored. Note that thread caching may prevent
some statistics from being completely up to date, since extra locking
would be required to merge counters that track thread cache operations.

The malloc_usable_size function returns the usable size of the
allocation pointed to by ptr. The return value may be larger than the
size that was requested during allocation. The malloc_usable_size
function is not a mechanism for in-place realloc; rather it is provided
solely as a tool for introspection purposes. Any discrepancy between
the requested allocation size and the size reported by
malloc_usable_size should not be depended on, since such behavior is
entirely implementation-dependent.

TUNING
Once, when the first call is made to one of the memory allocation
routines, the allocator initializes its internals based in part on
various options that can be specified at compile- or run-time.

The string specified via --with-malloc-conf, the string pointed to by
the global variable malloc_conf, the "name" of the file referenced by
the symbolic link named /etc/malloc.conf, and the value of the
environment variable MALLOC_CONF, will be interpreted, in that order,
from left to right as options. Note that malloc_conf may be read before
main is entered, so the declaration of malloc_conf should specify an
initializer that contains the final value to be read by jemalloc.
--with-malloc-conf and malloc_conf are compile-time mechanisms, whereas
/etc/malloc.conf and MALLOC_CONF can be safely set any time prior to
program invocation.

An options string is a comma-separated list of option:value pairs.
There is one key corresponding to each "opt.*" mallctl (see the MALLCTL
NAMESPACE section for options documentation). For example,
abort:true,narenas:1 sets the "opt.abort" and "opt.narenas" options.
Some options have boolean values (true/false), others have integer
values (base 8, 10, or 16, depending on prefix), and yet others have
raw string values.

IMPLEMENTATION NOTES
Traditionally, allocators have used sbrk(2) to obtain memory, which is
suboptimal for several reasons, including race conditions, increased
fragmentation, and artificial limitations on maximum usable memory. If
sbrk(2) is supported by the operating system, this allocator uses both
mmap(2) and sbrk(2), in that order of preference; otherwise only
mmap(2) is used.

This allocator uses multiple arenas in order to reduce lock contention
for threaded programs on multi-processor systems. This works well with
regard to threading scalability, but incurs some costs. There is a
small fixed per-arena overhead, and additionally, arenas manage memory
completely independently of each other, which means a small fixed
increase in overall memory fragmentation. These overheads are not
generally an issue, given the number of arenas normally used. Note that
using substantially more arenas than the default is not likely to
improve performance, mainly due to reduced cache performance. However,
it may make sense to reduce the number of arenas if an application does
not make much use of the allocation functions.

In addition to multiple arenas, unless --disable-tcache is specified
during configuration, this allocator supports thread-specific caching
for small and large objects, in order to make it possible to completely
avoid synchronization for most allocation requests. Such caching allows
very fast allocation in the common case, but it increases memory usage
and fragmentation, since a bounded number of objects can remain
allocated in each thread cache.

Memory is conceptually broken into equal-sized chunks, where the chunk
size is a power of two that is greater than the page size. Chunks are
always aligned to multiples of the chunk size. This alignment makes it
possible to find metadata for user objects very quickly. User objects
are broken into three categories according to size: small, large, and
huge. Multiple small and large objects can reside within a single
chunk, whereas huge objects each have one or more chunks backing them.
Each chunk that contains small and/or large objects tracks its contents
as runs of contiguous pages (unused, backing a set of small objects, or
backing one large object). The combination of chunk alignment and chunk
page maps makes it possible to determine all metadata regarding small
and large allocations in constant time.

Small objects are managed in groups by page runs. Each run maintains a
bitmap to track which regions are in use. Allocation requests that are
no more than half the quantum (8 or 16, depending on architecture) are
rounded up to the nearest power of two that is at least sizeof(double).
All other object size classes are multiples of the quantum, spaced such
that there are four size classes for each doubling in size, which
limits internal fragmentation to approximately 20% for all but the
smallest size classes. Small size classes are smaller than four times
the page size, large size classes are smaller than the chunk size (see
the "opt.lg_chunk" option), and huge size classes extend from the chunk
size up to the largest size class that does not exceed PTRDIFF_MAX.

Allocations are packed tightly together, which can be an issue for
multi-threaded applications. If you need to assure that allocations do
not suffer from cacheline sharing, round your allocation requests up to
the nearest multiple of the cacheline size, or specify cacheline
alignment when allocating.

The realloc, rallocx, and xallocx functions may resize allocations
without moving them under limited circumstances. Unlike the *allocx
API, the standard API does not officially round up the usable size of
an allocation to the nearest size class, so technically it is necessary
to call realloc to grow e.g. a 9-byte allocation to 16 bytes, or shrink
a 16-byte allocation to 9 bytes. Growth and shrinkage trivially
succeeds in place as long as the pre-size and post-size both round up
to the same size class. No other API guarantees are made regarding
in-place resizing, but the current implementation also tries to resize
large and huge allocations in place, as long as the pre-size and
post-size are both large or both huge. In such cases shrinkage always
succeeds for large size classes, but for huge size classes the chunk
allocator must support splitting (see "arena.<i>.chunk_hooks"). Growth
only succeeds if the trailing memory is currently available, and
additionally for huge size classes the chunk allocator must support
merging.

Assuming 2 MiB chunks, 4 KiB pages, and a 16-byte quantum on a 64-bit
system, the size classes in each category are as shown in Table 1.

Table 1. Size classes

+---------+---------+---------------------+
|Category | Spacing | Size |
+---------+---------+---------------------+
|Small | lg | [8] |
+---------+---------+---------------------+
| | 16 | [16, 32, 48, 64, |
| | | 80, 96, 112, 128] |
+---------+---------+---------------------+
| | 32 | [160, 192, 224, |
| | | 256] |
+---------+---------+---------------------+
| | 64 | [320, 384, 448, |
| | | 512] |
+---------+---------+---------------------+
| | 128 | [640, 768, 896, |
| | | 1024] |
+---------+---------+---------------------+
| | 256 | [1280, 1536, 1792, |
| | | 2048] |
+---------+---------+---------------------+
| | 512 | [2560, 3072, 3584, |
| | | 4096] |
+---------+---------+---------------------+
| | 1 KiB | [5 KiB, 6 KiB, 7 |
| | | KiB, 8 KiB] |
+---------+---------+---------------------+
| | 2 KiB | [10 KiB, 12 KiB, 14 |
| | | KiB] |
+---------+---------+---------------------+
|Large | 2 KiB | [16 KiB] |
+---------+---------+---------------------+
| | 4 KiB | [20 KiB, 24 KiB, 28 |
| | | KiB, 32 KiB] |
+---------+---------+---------------------+
| | 8 KiB | [40 KiB, 48 KiB, 54 |
| | | KiB, 64 KiB] |
+---------+---------+---------------------+
| | 16 KiB | [80 KiB, 96 KiB, |
| | | 112 KiB, 128 KiB] |
+---------+---------+---------------------+
| | 32 KiB | [160 KiB, 192 KiB, |
| | | 224 KiB, 256 KiB] |
+---------+---------+---------------------+
| | 64 KiB | [320 KiB, 384 KiB, |
| | | 448 KiB, 512 KiB] |
+---------+---------+---------------------+
| | 128 KiB | [640 KiB, 768 KiB, |
| | | 896 KiB, 1 MiB] |
+---------+---------+---------------------+
| | 256 KiB | [1280 KiB, 1536 |
| | | KiB, 1792 KiB] |
+---------+---------+---------------------+
|Huge | 256 KiB | [2 MiB] |
+---------+---------+---------------------+
| | 512 KiB | [2560 KiB, 3 MiB, |
| | | 3584 KiB, 4 MiB] |
+---------+---------+---------------------+
| | 1 MiB | [5 MiB, 6 MiB, 7 |
| | | MiB, 8 MiB] |
+---------+---------+---------------------+
| | 2 MiB | [10 MiB, 12 MiB, 14 |
| | | MiB, 16 MiB] |
+---------+---------+---------------------+
| | 4 MiB | [20 MiB, 24 MiB, 28 |
| | | MiB, 32 MiB] |
+---------+---------+---------------------+
| | 8 MiB | [40 MiB, 48 MiB, 56 |
| | | MiB, 64 MiB] |
+---------+---------+---------------------+
| | ... | ... |
+---------+---------+---------------------+
| | 512 PiB | [2560 PiB, 3 EiB, |
| | | 3584 PiB, 4 EiB] |
+---------+---------+---------------------+
| | 1 EiB | [5 EiB, 6 EiB, 7 |
| | | EiB] |
+---------+---------+---------------------+

MALLCTL NAMESPACE
The following names are defined in the namespace accessible via the
mallctl* functions. Value types are specified in parentheses, their
readable/writable statuses are encoded as rw, r-, -w, or --, and
required build configuration flags follow, if any. A name element
encoded as <i> or <j> indicates an integer component, where the integer
varies from 0 to some upper value that must be determined via
introspection. In the case of "stats.arenas.<i>.*", <i> equal to
"arenas.narenas" can be used to access the summation of statistics from
all arenas. Take special note of the "epoch" mallctl, which controls
refreshing of cached dynamic statistics.

"version" (const char *) r-
Return the jemalloc version string.

"epoch" (uint64_t) rw
If a value is passed in, refresh the data from which the mallctl*
functions report values, and increment the epoch. Return the
current epoch. This is useful for detecting whether another thread
caused a refresh.

"config.cache_oblivious" (bool) r-
--enable-cache-oblivious was specified during build configuration.

"config.debug" (bool) r-
--enable-debug was specified during build configuration.

"config.fill" (bool) r-
--enable-fill was specified during build configuration.

"config.lazy_lock" (bool) r-
--enable-lazy-lock was specified during build configuration.

"config.malloc_conf" (const char *) r-
Embedded configure-time-specified run-time options string, empty
unless --with-malloc-conf was specified during build configuration.

"config.munmap" (bool) r-
--enable-munmap was specified during build configuration.

"config.prof" (bool) r-
--enable-prof was specified during build configuration.

"config.prof_libgcc" (bool) r-
--disable-prof-libgcc was not specified during build configuration.

"config.prof_libunwind" (bool) r-
--enable-prof-libunwind was specified during build configuration.

"config.stats" (bool) r-
--enable-stats was specified during build configuration.

"config.tcache" (bool) r-
--disable-tcache was not specified during build configuration.

"config.tls" (bool) r-
--disable-tls was not specified during build configuration.

"config.utrace" (bool) r-
--enable-utrace was specified during build configuration.

"config.valgrind" (bool) r-
--enable-valgrind was specified during build configuration.

"config.xmalloc" (bool) r-
--enable-xmalloc was specified during build configuration.

"opt.abort" (bool) r-
Abort-on-warning enabled/disabled. If true, most warnings are
fatal. The process will call abort(3) in these cases. This option
is disabled by default unless --enable-debug is specified during
configuration, in which case it is enabled by default.

"opt.dss" (const char *) r-
dss (sbrk(2)) allocation precedence as related to mmap(2)
allocation. The following settings are supported if sbrk(2) is
supported by the operating system: "disabled", "primary", and
"secondary"; otherwise only "disabled" is supported. The default is
"secondary" if sbrk(2) is supported by the operating system;
"disabled" otherwise.

"opt.lg_chunk" (size_t) r-
Virtual memory chunk size (log base 2). If a chunk size outside the
supported size range is specified, the size is silently clipped to
the minimum/maximum supported size. The default chunk size is 2 MiB
(2^21).

"opt.narenas" (unsigned) r-
Maximum number of arenas to use for automatic multiplexing of
threads and arenas. The default is four times the number of CPUs,
or one if there is a single CPU.

"opt.purge" (const char *) r-
Purge mode is "ratio" (default) or "decay". See "opt.lg_dirty_mult"
for details of the ratio mode. See "opt.decay_time" for details of
the decay mode.

"opt.lg_dirty_mult" (ssize_t) r-
Per-arena minimum ratio (log base 2) of active to dirty pages. Some
dirty unused pages may be allowed to accumulate, within the limit
set by the ratio (or one chunk worth of dirty pages, whichever is
greater), before informing the kernel about some of those pages via
madvise(2) or a similar system call. This provides the kernel with
sufficient information to recycle dirty pages if physical memory
becomes scarce and the pages remain unused. The default minimum
ratio is 8:1 (2^3:1); an option value of -1 will disable dirty page
purging. See "arenas.lg_dirty_mult" and "arena.<i>.lg_dirty_mult"
for related dynamic control options.

"opt.decay_time" (ssize_t) r-
Approximate time in seconds from the creation of a set of unused
dirty pages until an equivalent set of unused dirty pages is purged
and/or reused. The pages are incrementally purged according to a
sigmoidal decay curve that starts and ends with zero purge rate. A
decay time of 0 causes all unused dirty pages to be purged
immediately upon creation. A decay time of -1 disables purging. The
default decay time is 10 seconds. See "arenas.decay_time" and
"arena.<i>.decay_time" for related dynamic control options.

"opt.stats_print" (bool) r-
Enable/disable statistics printing at exit. If enabled, the
malloc_stats_print function is called at program exit via an
atexit(3) function. If --enable-stats is specified during
configuration, this has the potential to cause deadlock for a
multi-threaded process that exits while one or more threads are
executing in the memory allocation functions. Furthermore, atexit
may allocate memory during application initialization and then
deadlock internally when jemalloc in turn calls atexit, so this
option is not universally usable (though the application can
register its own atexit function with equivalent functionality).
Therefore, this option should only be used with care; it is
primarily intended as a performance tuning aid during application
development. This option is disabled by default.

"opt.junk" (const char *) r- [--enable-fill]
Junk filling. If set to "alloc", each byte of uninitialized
allocated memory will be initialized to 0xa5. If set to "free", all
deallocated memory will be initialized to 0x5a. If set to "true",
both allocated and deallocated memory will be initialized, and if
set to "false", junk filling be disabled entirely. This is intended
for debugging and will impact performance negatively. This option
is "false" by default unless --enable-debug is specified during
configuration, in which case it is "true" by default unless running
inside Valgrind[2].

"opt.quarantine" (size_t) r- [--enable-fill]
Per thread quarantine size in bytes. If non-zero, each thread
maintains a FIFO object quarantine that stores up to the specified
number of bytes of memory. The quarantined memory is not freed
until it is released from quarantine, though it is immediately
junk-filled if the "opt.junk" option is enabled. This feature is of
particular use in combination with Valgrind[2], which can detect
attempts to access quarantined objects. This is intended for
debugging and will impact performance negatively. The default
quarantine size is 0 unless running inside Valgrind, in which case
the default is 16 MiB.

"opt.redzone" (bool) r- [--enable-fill]
Redzones enabled/disabled. If enabled, small allocations have
redzones before and after them. Furthermore, if the "opt.junk"
option is enabled, the redzones are checked for corruption during
deallocation. However, the primary intended purpose of this feature
is to be used in combination with Valgrind[2], which needs redzones
in order to do effective buffer overflow/underflow detection. This
option is intended for debugging and will impact performance
negatively. This option is disabled by default unless running
inside Valgrind.

"opt.zero" (bool) r- [--enable-fill]
Zero filling enabled/disabled. If enabled, each byte of
uninitialized allocated memory will be initialized to 0. Note that
this initialization only happens once for each byte, so realloc and
rallocx calls do not zero memory that was previously allocated.
This is intended for debugging and will impact performance
negatively. This option is disabled by default.

"opt.utrace" (bool) r- [--enable-utrace]
Allocation tracing based on utrace(2) enabled/disabled. This option
is disabled by default.

"opt.xmalloc" (bool) r- [--enable-xmalloc]
Abort-on-out-of-memory enabled/disabled. If enabled, rather than
returning failure for any allocation function, display a diagnostic
message on STDERR_FILENO and cause the program to drop core (using
abort(3)). If an application is designed to depend on this
behavior, set the option at compile time by including the following
in the source code:

malloc_conf = "xmalloc:true";

This option is disabled by default.

"opt.tcache" (bool) r- [--enable-tcache]
Thread-specific caching (tcache) enabled/disabled. When there are
multiple threads, each thread uses a tcache for objects up to a
certain size. Thread-specific caching allows many allocations to be
satisfied without performing any thread synchronization, at the
cost of increased memory use. See the "opt.lg_tcache_max" option
for related tuning information. This option is enabled by default
unless running inside Valgrind[2], in which case it is forcefully
disabled.

"opt.lg_tcache_max" (size_t) r- [--enable-tcache]
Maximum size class (log base 2) to cache in the thread-specific
cache (tcache). At a minimum, all small size classes are cached,
and at a maximum all large size classes are cached. The default
maximum is 32 KiB (2^15).

"opt.prof" (bool) r- [--enable-prof]
Memory profiling enabled/disabled. If enabled, profile memory
allocation activity. See the "opt.prof_active" option for
on-the-fly activation/deactivation. See the "opt.lg_prof_sample"
option for probabilistic sampling control. See the "opt.prof_accum"
option for control of cumulative sample reporting. See the
"opt.lg_prof_interval" option for information on interval-triggered
profile dumping, the "opt.prof_gdump" option for information on
high-water-triggered profile dumping, and the "opt.prof_final"
option for final profile dumping. Profile output is compatible with
the jeprof command, which is based on the pprof that is developed
as part of the gperftools package[3]. See HEAP PROFILE FORMAT for
heap profile format documentation.

"opt.prof_prefix" (const char *) r- [--enable-prof]
Filename prefix for profile dumps. If the prefix is set to the
empty string, no automatic dumps will occur; this is primarily
useful for disabling the automatic final heap dump (which also
disables leak reporting, if enabled). The default prefix is jeprof.

"opt.prof_active" (bool) r- [--enable-prof]
Profiling activated/deactivated. This is a secondary control
mechanism that makes it possible to start the application with
profiling enabled (see the "opt.prof" option) but inactive, then
toggle profiling at any time during program execution with the
"prof.active" mallctl. This option is enabled by default.

"opt.prof_thread_active_init" (bool) r- [--enable-prof]
Initial setting for "thread.prof.active" in newly created threads.
The initial setting for newly created threads can also be changed
during execution via the "prof.thread_active_init" mallctl. This
option is enabled by default.

"opt.lg_prof_sample" (size_t) r- [--enable-prof]
Average interval (log base 2) between allocation samples, as
measured in bytes of allocation activity. Increasing the sampling
interval decreases profile fidelity, but also decreases the
computational overhead. The default sample interval is 512 KiB
(2^19 B).

"opt.prof_accum" (bool) r- [--enable-prof]
Reporting of cumulative object/byte counts in profile dumps
enabled/disabled. If this option is enabled, every unique backtrace
must be stored for the duration of execution. Depending on the
application, this can impose a large memory overhead, and the
cumulative counts are not always of interest. This option is
disabled by default.

"opt.lg_prof_interval" (ssize_t) r- [--enable-prof]
Average interval (log base 2) between memory profile dumps, as
measured in bytes of allocation activity. The actual interval
between dumps may be sporadic because decentralized allocation
counters are used to avoid synchronization bottlenecks. Profiles
are dumped to files named according to the pattern
<prefix>.<pid>.<seq>.i<iseq>.heap, where <prefix> is controlled by
the "opt.prof_prefix" option. By default, interval-triggered
profile dumping is disabled (encoded as -1).

"opt.prof_gdump" (bool) r- [--enable-prof]
Set the initial state of "prof.gdump", which when enabled triggers
a memory profile dump every time the total virtual memory exceeds
the previous maximum. This option is disabled by default.

"opt.prof_final" (bool) r- [--enable-prof]
Use an atexit(3) function to dump final memory usage to a file
named according to the pattern <prefix>.<pid>.<seq>.f.heap, where
<prefix> is controlled by the "opt.prof_prefix" option. Note that
atexit may allocate memory during application initialization and
then deadlock internally when jemalloc in turn calls atexit, so
this option is not universally usable (though the application can
register its own atexit function with equivalent functionality).
This option is disabled by default.

"opt.prof_leak" (bool) r- [--enable-prof]
Leak reporting enabled/disabled. If enabled, use an atexit(3)
function to report memory leaks detected by allocation sampling.
See the "opt.prof" option for information on analyzing heap profile
output. This option is disabled by default.

"thread.arena" (unsigned) rw
Get or set the arena associated with the calling thread. If the
specified arena was not initialized beforehand (see the
"arenas.initialized" mallctl), it will be automatically initialized
as a side effect of calling this interface.

"thread.allocated" (uint64_t) r- [--enable-stats]
Get the total number of bytes ever allocated by the calling thread.
This counter has the potential to wrap around; it is up to the
application to appropriately interpret the counter in such cases.

"thread.allocatedp" (uint64_t *) r- [--enable-stats]
Get a pointer to the the value that is returned by the
"thread.allocated" mallctl. This is useful for avoiding the
overhead of repeated mallctl* calls.

"thread.deallocated" (uint64_t) r- [--enable-stats]
Get the total number of bytes ever deallocated by the calling
thread. This counter has the potential to wrap around; it is up to
the application to appropriately interpret the counter in such
cases.

"thread.deallocatedp" (uint64_t *) r- [--enable-stats]
Get a pointer to the the value that is returned by the
"thread.deallocated" mallctl. This is useful for avoiding the
overhead of repeated mallctl* calls.

"thread.tcache.enabled" (bool) rw [--enable-tcache]
Enable/disable calling thread's tcache. The tcache is implicitly
flushed as a side effect of becoming disabled (see
"thread.tcache.flush").

"thread.tcache.flush" (void) -- [--enable-tcache]
Flush calling thread's thread-specific cache (tcache). This
interface releases all cached objects and internal data structures
associated with the calling thread's tcache. Ordinarily, this
interface need not be called, since automatic periodic incremental
garbage collection occurs, and the thread cache is automatically
discarded when a thread exits. However, garbage collection is
triggered by allocation activity, so it is possible for a thread
that stops allocating/deallocating to retain its cache
indefinitely, in which case the developer may find manual flushing
useful.

"thread.prof.name" (const char *) r- or -w [--enable-prof]
Get/set the descriptive name associated with the calling thread in
memory profile dumps. An internal copy of the name string is
created, so the input string need not be maintained after this
interface completes execution. The output string of this interface
should be copied for non-ephemeral uses, because multiple
implementation details can cause asynchronous string deallocation.
Furthermore, each invocation of this interface can only read or
write; simultaneous read/write is not supported due to string
lifetime limitations. The name string must be nil-terminated and
comprised only of characters in the sets recognized by isgraph(3)
and isblank(3).

"thread.prof.active" (bool) rw [--enable-prof]
Control whether sampling is currently active for the calling
thread. This is an activation mechanism in addition to
"prof.active"; both must be active for the calling thread to
sample. This flag is enabled by default.

"tcache.create" (unsigned) r- [--enable-tcache]
Create an explicit thread-specific cache (tcache) and return an
identifier that can be passed to the MALLOCX_TCACHE(tc) macro to
explicitly use the specified cache rather than the automatically
managed one that is used by default. Each explicit cache can be
used by only one thread at a time; the application must assure that
this constraint holds.

"tcache.flush" (unsigned) -w [--enable-tcache]
Flush the specified thread-specific cache (tcache). The same
considerations apply to this interface as to "thread.tcache.flush",
except that the tcache will never be automatically discarded.

"tcache.destroy" (unsigned) -w [--enable-tcache]
Flush the specified thread-specific cache (tcache) and make the
identifier available for use during a future tcache creation.

"arena.<i>.purge" (void) --
Purge all unused dirty pages for arena <i>, or for all arenas if
<i> equals "arenas.narenas".

"arena.<i>.decay" (void) --
Trigger decay-based purging of unused dirty pages for arena <i>, or
for all arenas if <i> equals "arenas.narenas". The proportion of
unused dirty pages to be purged depends on the current time; see
"opt.decay_time" for details.

"arena.<i>.reset" (void) --
Discard all of the arena's extant allocations. This interface can
only be used with arenas created via "arenas.extend". None of the
arena's discarded/cached allocations may accessed afterward. As
part of this requirement, all thread caches which were used to
allocate/deallocate in conjunction with the arena must be flushed
beforehand. This interface cannot be used if running inside
Valgrind, nor if the quarantine size is non-zero.

"arena.<i>.dss" (const char *) rw
Set the precedence of dss allocation as related to mmap allocation
for arena <i>, or for all arenas if <i> equals "arenas.narenas".
See "opt.dss" for supported settings.

"arena.<i>.lg_dirty_mult" (ssize_t) rw
Current per-arena minimum ratio (log base 2) of active to dirty
pages for arena <i>. Each time this interface is set and the ratio
is increased, pages are synchronously purged as necessary to impose
the new ratio. See "opt.lg_dirty_mult" for additional information.

"arena.<i>.decay_time" (ssize_t) rw
Current per-arena approximate time in seconds from the creation of
a set of unused dirty pages until an equivalent set of unused dirty
pages is purged and/or reused. Each time this interface is set, all
currently unused dirty pages are considered to have fully decayed,
which causes immediate purging of all unused dirty pages unless the
decay time is set to -1 (i.e. purging disabled). See
"opt.decay_time" for additional information.

"arena.<i>.chunk_hooks" (chunk_hooks_t) rw
Get or set the chunk management hook functions for arena <i>. The
functions must be capable of operating on all extant chunks
associated with arena <i>, usually by passing unknown chunks to the
replaced functions. In practice, it is feasible to control
allocation for arenas created via "arenas.extend" such that all
chunks originate from an application-supplied chunk allocator (by
setting custom chunk hook functions just after arena creation), but
the automatically created arenas may have already created chunks
prior to the application having an opportunity to take over chunk
allocation.

typedef struct {
chunk_alloc_t *alloc;
chunk_dalloc_t *dalloc;
chunk_commit_t *commit;
chunk_decommit_t *decommit;
chunk_purge_t *purge;
chunk_split_t *split;
chunk_merge_t *merge;
} chunk_hooks_t;

The chunk_hooks_t structure comprises function pointers which are
described individually below. jemalloc uses these functions to
manage chunk lifetime, which starts off with allocation of mapped
committed memory, in the simplest case followed by deallocation.
However, there are performance and platform reasons to retain
chunks for later reuse. Cleanup attempts cascade from deallocation
to decommit to purging, which gives the chunk management functions
opportunities to reject the most permanent cleanup operations in
favor of less permanent (and often less costly) operations. The
chunk splitting and merging operations can also be opted out of,
but this is mainly intended to support platforms on which virtual
memory mappings provided by the operating system kernel do not
automatically coalesce and split, e.g. Windows.

typedef void *(chunk_alloc_t)(void *chunk, size_t size,
size_t alignment, bool *zero,
bool *commit, unsigned arena_ind);

A chunk allocation function conforms to the chunk_alloc_t type and
upon success returns a pointer to size bytes of mapped memory on
behalf of arena arena_ind such that the chunk's base address is a
multiple of alignment, as well as setting *zero to indicate whether
the chunk is zeroed and *commit to indicate whether the chunk is
committed. Upon error the function returns NULL and leaves *zero
and *commit unmodified. The size parameter is always a multiple of
the chunk size. The alignment parameter is always a power of two at
least as large as the chunk size. Zeroing is mandatory if *zero is
true upon function entry. Committing is mandatory if *commit is
true upon function entry. If chunk is not NULL, the returned
pointer must be chunk on success or NULL on error. Committed memory
may be committed in absolute terms as on a system that does not
overcommit, or in implicit terms as on a system that overcommits
and satisfies physical memory needs on demand via soft page faults.
Note that replacing the default chunk allocation function makes the
arena's "arena.<i>.dss" setting irrelevant.

typedef bool (chunk_dalloc_t)(void *chunk, size_t size,
bool committed, unsigned arena_ind);

A chunk deallocation function conforms to the chunk_dalloc_t type
and deallocates a chunk of given size with committed/decommited
memory as indicated, on behalf of arena arena_ind, returning false
upon success. If the function returns true, this indicates opt-out
from deallocation; the virtual memory mapping associated with the
chunk remains mapped, in the same commit state, and available for
future use, in which case it will be automatically retained for
later reuse.

typedef bool (chunk_commit_t)(void *chunk, size_t size,
size_t offset, size_t length,
unsigned arena_ind);

A chunk commit function conforms to the chunk_commit_t type and
commits zeroed physical memory to back pages within a chunk of
given size at offset bytes, extending for length on behalf of arena
arena_ind, returning false upon success. Committed memory may be
committed in absolute terms as on a system that does not
overcommit, or in implicit terms as on a system that overcommits
and satisfies physical memory needs on demand via soft page faults.
If the function returns true, this indicates insufficient physical
memory to satisfy the request.

typedef bool (chunk_decommit_t)(void *chunk, size_t size,
size_t offset, size_t length,
unsigned arena_ind);

A chunk decommit function conforms to the chunk_decommit_t type and
decommits any physical memory that is backing pages within a chunk
of given size at offset bytes, extending for length on behalf of
arena arena_ind, returning false upon success, in which case the
pages will be committed via the chunk commit function before being
reused. If the function returns true, this indicates opt-out from
decommit; the memory remains committed and available for future
use, in which case it will be automatically retained for later
reuse.

typedef bool (chunk_purge_t)(void *chunk, size_tsize,
size_t offset, size_t length,
unsigned arena_ind);

A chunk purge function conforms to the chunk_purge_t type and
optionally discards physical pages within the virtual memory
mapping associated with chunk of given size at offset bytes,
extending for length on behalf of arena arena_ind, returning false
if pages within the purged virtual memory range will be zero-filled
the next time they are accessed.

typedef bool (chunk_split_t)(void *chunk, size_t size,
size_t size_a, size_t size_b,
bool committed, unsigned arena_ind);

A chunk split function conforms to the chunk_split_t type and
optionally splits chunk of given size into two adjacent chunks, the
first of size_a bytes, and the second of size_b bytes, operating on
committed/decommitted memory as indicated, on behalf of arena
arena_ind, returning false upon success. If the function returns
true, this indicates that the chunk remains unsplit and therefore
should continue to be operated on as a whole.

typedef bool (chunk_merge_t)(void *chunk_a, size_t size_a,
void *chunk_b, size_t size_b,
bool committed, unsigned arena_ind);

A chunk merge function conforms to the chunk_merge_t type and
optionally merges adjacent chunks, chunk_a of given size_a and
chunk_b of given size_b into one contiguous chunk, operating on
committed/decommitted memory as indicated, on behalf of arena
arena_ind, returning false upon success. If the function returns
true, this indicates that the chunks remain distinct mappings and
therefore should continue to be operated on independently.

"arenas.narenas" (unsigned) r-
Current limit on number of arenas.

"arenas.initialized" (bool *) r-
An array of "arenas.narenas" booleans. Each boolean indicates
whether the corresponding arena is initialized.

"arenas.lg_dirty_mult" (ssize_t) rw
Current default per-arena minimum ratio (log base 2) of active to
dirty pages, used to initialize "arena.<i>.lg_dirty_mult" during
arena creation. See "opt.lg_dirty_mult" for additional information.

"arenas.decay_time" (ssize_t) rw
Current default per-arena approximate time in seconds from the
creation of a set of unused dirty pages until an equivalent set of
unused dirty pages is purged and/or reused, used to initialize
"arena.<i>.decay_time" during arena creation. See "opt.decay_time"
for additional information.

"arenas.quantum" (size_t) r-
Quantum size.

"arenas.page" (size_t) r-
Page size.

"arenas.tcache_max" (size_t) r- [--enable-tcache]
Maximum thread-cached size class.

"arenas.nbins" (unsigned) r-
Number of bin size classes.

"arenas.nhbins" (unsigned) r- [--enable-tcache]
Total number of thread cache bin size classes.

"arenas.bin.<i>.size" (size_t) r-
Maximum size supported by size class.

"arenas.bin.<i>.nregs" (uint32_t) r-
Number of regions per page run.

"arenas.bin.<i>.run_size" (size_t) r-
Number of bytes per page run.

"arenas.nlruns" (unsigned) r-
Total number of large size classes.

"arenas.lrun.<i>.size" (size_t) r-
Maximum size supported by this large size class.

"arenas.nhchunks" (unsigned) r-
Total number of huge size classes.

"arenas.hchunk.<i>.size" (size_t) r-
Maximum size supported by this huge size class.

"arenas.extend" (unsigned) r-
Extend the array of arenas by appending a new arena, and returning
the new arena index.

"prof.thread_active_init" (bool) rw [--enable-prof]
Control the initial setting for "thread.prof.active" in newly
created threads. See the "opt.prof_thread_active_init" option for
additional information.

"prof.active" (bool) rw [--enable-prof]
Control whether sampling is currently active. See the
"opt.prof_active" option for additional information, as well as the
interrelated "thread.prof.active" mallctl.

"prof.dump" (const char *) -w [--enable-prof]
Dump a memory profile to the specified file, or if NULL is
specified, to a file according to the pattern
<prefix>.<pid>.<seq>.m<mseq>.heap, where <prefix> is controlled by
the "opt.prof_prefix" option.

"prof.gdump" (bool) rw [--enable-prof]
When enabled, trigger a memory profile dump every time the total
virtual memory exceeds the previous maximum. Profiles are dumped to
files named according to the pattern
<prefix>.<pid>.<seq>.u<useq>.heap, where <prefix> is controlled by
the "opt.prof_prefix" option.

"prof.reset" (size_t) -w [--enable-prof]
Reset all memory profile statistics, and optionally update the
sample rate (see "opt.lg_prof_sample" and "prof.lg_sample").

"prof.lg_sample" (size_t) r- [--enable-prof]
Get the current sample rate (see "opt.lg_prof_sample").

"prof.interval" (uint64_t) r- [--enable-prof]
Average number of bytes allocated between interval-based profile
dumps. See the "opt.lg_prof_interval" option for additional
information.

"stats.cactive" (size_t *) r- [--enable-stats]
Pointer to a counter that contains an approximate count of the
current number of bytes in active pages. The estimate may be high,
but never low, because each arena rounds up when computing its
contribution to the counter. Note that the "epoch" mallctl has no
bearing on this counter. Furthermore, counter consistency is
maintained via atomic operations, so it is necessary to use an
atomic operation in order to guarantee a consistent read when
dereferencing the pointer.

"stats.allocated" (size_t) r- [--enable-stats]
Total number of bytes allocated by the application.

"stats.active" (size_t) r- [--enable-stats]
Total number of bytes in active pages allocated by the application.
This is a multiple of the page size, and greater than or equal to
"stats.allocated". This does not include "stats.arenas.<i>.pdirty",
nor pages entirely devoted to allocator metadata.

"stats.metadata" (size_t) r- [--enable-stats]
Total number of bytes dedicated to metadata, which comprise base
allocations used for bootstrap-sensitive internal allocator data
structures, arena chunk headers (see
"stats.arenas.<i>.metadata.mapped"), and internal allocations (see
"stats.arenas.<i>.metadata.allocated").

"stats.resident" (size_t) r- [--enable-stats]
Maximum number of bytes in physically resident data pages mapped by
the allocator, comprising all pages dedicated to allocator
metadata, pages backing active allocations, and unused dirty pages.
This is a maximum rather than precise because pages may not
actually be physically resident if they correspond to demand-zeroed
virtual memory that has not yet been touched. This is a multiple of
the page size, and is larger than "stats.active".

"stats.mapped" (size_t) r- [--enable-stats]
Total number of bytes in active chunks mapped by the allocator.
This is a multiple of the chunk size, and is larger than
"stats.active". This does not include inactive chunks, even those
that contain unused dirty pages, which means that there is no
strict ordering between this and "stats.resident".

"stats.retained" (size_t) r- [--enable-stats]
Total number of bytes in virtual memory mappings that were retained
rather than being returned to the operating system via e.g.
munmap(2). Retained virtual memory is typically untouched,
decommitted, or purged, so it has no strongly associated physical
memory (see chunk hooks for details). Retained memory is excluded
from mapped memory statistics, e.g. "stats.mapped".

"stats.arenas.<i>.dss" (const char *) r-
dss (sbrk(2)) allocation precedence as related to mmap(2)
allocation. See "opt.dss" for details.

"stats.arenas.<i>.lg_dirty_mult" (ssize_t) r-
Minimum ratio (log base 2) of active to dirty pages. See
"opt.lg_dirty_mult" for details.

"stats.arenas.<i>.decay_time" (ssize_t) r-
Approximate time in seconds from the creation of a set of unused
dirty pages until an equivalent set of unused dirty pages is purged
and/or reused. See "opt.decay_time" for details.

"stats.arenas.<i>.nthreads" (unsigned) r-
Number of threads currently assigned to arena.

"stats.arenas.<i>.pactive" (size_t) r-
Number of pages in active runs.

"stats.arenas.<i>.pdirty" (size_t) r-
Number of pages within unused runs that are potentially dirty, and
for which madvise... MADV_DONTNEED or similar has not been called.

"stats.arenas.<i>.mapped" (size_t) r- [--enable-stats]
Number of mapped bytes.

"stats.arenas.<i>.retained" (size_t) r- [--enable-stats]
Number of retained bytes. See "stats.retained" for details.

"stats.arenas.<i>.metadata.mapped" (size_t) r- [--enable-stats]
Number of mapped bytes in arena chunk headers, which track the
states of the non-metadata pages.

"stats.arenas.<i>.metadata.allocated" (size_t) r- [--enable-stats]
Number of bytes dedicated to internal allocations. Internal
allocations differ from application-originated allocations in that
they are for internal use, and that they are omitted from heap
profiles. This statistic is reported separately from
"stats.metadata" and "stats.arenas.<i>.metadata.mapped" because it
overlaps with e.g. the "stats.allocated" and "stats.active"
statistics, whereas the other metadata statistics do not.

"stats.arenas.<i>.npurge" (uint64_t) r- [--enable-stats]
Number of dirty page purge sweeps performed.

"stats.arenas.<i>.nmadvise" (uint64_t) r- [--enable-stats]
Number of madvise... MADV_DONTNEED or similar calls made to purge
dirty pages.

"stats.arenas.<i>.purged" (uint64_t) r- [--enable-stats]
Number of pages purged.

"stats.arenas.<i>.small.allocated" (size_t) r- [--enable-stats]
Number of bytes currently allocated by small objects.

"stats.arenas.<i>.small.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests served by small bins.

"stats.arenas.<i>.small.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of small objects returned to bins.

"stats.arenas.<i>.small.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of small allocation requests.

"stats.arenas.<i>.large.allocated" (size_t) r- [--enable-stats]
Number of bytes currently allocated by large objects.

"stats.arenas.<i>.large.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of large allocation requests served directly by
the arena.

"stats.arenas.<i>.large.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of large deallocation requests served directly by
the arena.

"stats.arenas.<i>.large.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of large allocation requests.

"stats.arenas.<i>.huge.allocated" (size_t) r- [--enable-stats]
Number of bytes currently allocated by huge objects.

"stats.arenas.<i>.huge.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of huge allocation requests served directly by
the arena.

"stats.arenas.<i>.huge.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of huge deallocation requests served directly by
the arena.

"stats.arenas.<i>.huge.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of huge allocation requests.

"stats.arenas.<i>.bins.<j>.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of allocations served by bin.

"stats.arenas.<i>.bins.<j>.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of allocations returned to bin.

"stats.arenas.<i>.bins.<j>.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests.

"stats.arenas.<i>.bins.<j>.curregs" (size_t) r- [--enable-stats]
Current number of regions for this size class.

"stats.arenas.<i>.bins.<j>.nfills" (uint64_t) r- [--enable-stats
--enable-tcache]
Cumulative number of tcache fills.

"stats.arenas.<i>.bins.<j>.nflushes" (uint64_t) r- [--enable-stats
--enable-tcache]
Cumulative number of tcache flushes.

"stats.arenas.<i>.bins.<j>.nruns" (uint64_t) r- [--enable-stats]
Cumulative number of runs created.

"stats.arenas.<i>.bins.<j>.nreruns" (uint64_t) r- [--enable-stats]
Cumulative number of times the current run from which to allocate
changed.

"stats.arenas.<i>.bins.<j>.curruns" (size_t) r- [--enable-stats]
Current number of runs.

"stats.arenas.<i>.lruns.<j>.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests for this size class served
directly by the arena.

"stats.arenas.<i>.lruns.<j>.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of deallocation requests for this size class
served directly by the arena.

"stats.arenas.<i>.lruns.<j>.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests for this size class.

"stats.arenas.<i>.lruns.<j>.curruns" (size_t) r- [--enable-stats]
Current number of runs for this size class.

"stats.arenas.<i>.hchunks.<j>.nmalloc" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests for this size class served
directly by the arena.

"stats.arenas.<i>.hchunks.<j>.ndalloc" (uint64_t) r- [--enable-stats]
Cumulative number of deallocation requests for this size class
served directly by the arena.

"stats.arenas.<i>.hchunks.<j>.nrequests" (uint64_t) r- [--enable-stats]
Cumulative number of allocation requests for this size class.

"stats.arenas.<i>.hchunks.<j>.curhchunks" (size_t) r- [--enable-stats]
Current number of huge allocations for this size class.

HEAP PROFILE FORMAT
Although the heap profiling functionality was originally designed to be
compatible with the pprof command that is developed as part of the
gperftools package[3], the addition of per thread heap profiling
functionality required a different heap profile format. The jeprof
command is derived from pprof, with enhancements to support the heap
profile format described here.

In the following hypothetical heap profile, [...] indicates elision for
the sake of compactness.

heap_v2/524288
t*: 28106: 56637512 [0: 0]
[...]
t3: 352: 16777344 [0: 0]
[...]
t99: 17754: 29341640 [0: 0]
[...]
@ 0x5f86da8 0x5f5a1dc [...] 0x29e4d4e 0xa200316 0xabb2988 [...]
t*: 13: 6688 [0: 0]
t3: 12: 6496 [0: ]
t99: 1: 192 [0: 0]
[...]

MAPPED_LIBRARIES:
[...]

The following matches the above heap profile, but most tokens are
replaced with <description> to indicate descriptions of the
corresponding fields.

<heap_profile_format_version>/<mean_sample_interval>
<aggregate>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
[...]
<thread_3_aggregate>: <curobjs>: <curbytes>[<cumobjs>: <cumbytes>]
[...]
<thread_99_aggregate>: <curobjs>: <curbytes>[<cumobjs>: <cumbytes>]
[...]
@ <top_frame> <frame> [...] <frame> <frame> <frame> [...]
<backtrace_aggregate>: <curobjs>: <curbytes> [<cumobjs>:
<cumbytes>]
<backtrace_thread_3>: <curobjs>: <curbytes> [<cumobjs>: <cumbytes>]
<backtrace_thread_99>: <curobjs>: <curbytes> [<cumobjs>:
<cumbytes>]
[...]

MAPPED_LIBRARIES:
</proc/<pid>/maps>

DEBUGGING MALLOC PROBLEMS
When debugging, it is a good idea to configure/build jemalloc with the
--enable-debug and --enable-fill options, and recompile the program
with suitable options and symbols for debugger support. When so
configured, jemalloc incorporates a wide variety of run-time assertions
that catch application errors such as double-free, write-after-free,
etc.

Programs often accidentally depend on "uninitialized" memory actually
being filled with zero bytes. Junk filling (see the "opt.junk" option)
tends to expose such bugs in the form of obviously incorrect results
and/or coredumps. Conversely, zero filling (see the "opt.zero" option)
eliminates the symptoms of such bugs. Between these two options, it is
usually possible to quickly detect, diagnose, and eliminate such bugs.

This implementation does not provide much detail about the problems it
detects, because the performance impact for storing such information
would be prohibitive. However, jemalloc does integrate with the most
excellent Valgrind[2] tool if the --enable-valgrind configuration
option is enabled.

DIAGNOSTIC MESSAGES
If any of the memory allocation/deallocation functions detect an error
or warning condition, a message will be printed to file descriptor
STDERR_FILENO. Errors will result in the process dumping core. If the
"opt.abort" option is set, most warnings are treated as errors.

The malloc_message variable allows the programmer to override the
function which emits the text strings forming the errors and warnings
if for some reason the STDERR_FILENO file descriptor is not suitable
for this. malloc_message takes the cbopaque pointer argument that is
NULL unless overridden by the arguments in a call to
malloc_stats_print, followed by a string pointer. Please note that
doing anything which tries to allocate memory in this function is
likely to result in a crash or deadlock.

All messages are prefixed by "<jemalloc>:".

RETURN VALUES
Standard API
The malloc and calloc functions return a pointer to the allocated
memory if successful; otherwise a NULL pointer is returned and errno is
set to ENOMEM.

The posix_memalign function returns the value 0 if successful;
otherwise it returns an error value. The posix_memalign function will
fail if:

EINVAL
The alignment parameter is not a power of 2 at least as large as
sizeof(void *).

ENOMEM
Memory allocation error.

The aligned_alloc function returns a pointer to the allocated memory if
successful; otherwise a NULL pointer is returned and errno is set. The
aligned_alloc function will fail if:

EINVAL
The alignment parameter is not a power of 2.

ENOMEM
Memory allocation error.

The realloc function returns a pointer, possibly identical to ptr, to
the allocated memory if successful; otherwise a NULL pointer is
returned, and errno is set to ENOMEM if the error was the result of an
allocation failure. The realloc function always leaves the original
buffer intact when an error occurs.

The free function returns no value.

Non-standard API
The mallocx and rallocx functions return a pointer to the allocated
memory if successful; otherwise a NULL pointer is returned to indicate
insufficient contiguous memory was available to service the allocation
request.

The xallocx function returns the real size of the resulting resized
allocation pointed to by ptr, which is a value less than size if the
allocation could not be adequately grown in place.

The sallocx function returns the real size of the allocation pointed to
by ptr.

The nallocx returns the real size that would result from a successful
equivalent mallocx function call, or zero if insufficient memory is
available to perform the size computation.

The mallctl, mallctlnametomib, and mallctlbymib functions return 0 on
success; otherwise they return an error value. The functions will fail
if:

EINVAL
newp is not NULL, and newlen is too large or too small.
Alternatively, *oldlenp is too large or too small; in this case as
much data as possible are read despite the error.

ENOENT
name or mib specifies an unknown/invalid value.

EPERM
Attempt to read or write void value, or attempt to write read-only
value.

EAGAIN
A memory allocation failure occurred.

EFAULT
An interface with side effects failed in some way not directly
related to mallctl* read/write processing.

The malloc_usable_size function returns the usable size of the
allocation pointed to by ptr.

ENVIRONMENT
The following environment variable affects the execution of the
allocation functions:

MALLOC_CONF
If the environment variable MALLOC_CONF is set, the characters it
contains will be interpreted as options.

EXAMPLES
To dump core whenever a problem occurs:

ln -s 'abort:true' /etc/malloc.conf

To specify in the source a chunk size that is 16 MiB:

malloc_conf = "lg_chunk:24";

SEE ALSO
madvise(2), mmap(2), sbrk(2), utrace(2), alloca(3), atexit(3),
getpagesize(3)

STANDARDS
The malloc, calloc, realloc, and free functions conform to ISO/IEC
9899:1990 ("ISO C90").

The posix_memalign function conforms to IEEE Std 1003.1-2001
("POSIX.1").

HISTORY
The malloc_usable_size and posix_memalign functions first appeared in
FreeBSD 7.0.

The aligned_alloc, malloc_stats_print, and mallctl* functions first
appeared in FreeBSD 10.0.

The *allocx functions first appeared in FreeBSD 11.0.

AUTHOR
Jason Evans

NOTES
1. jemalloc website


2. Valgrind


3. gperftools package


jemalloc 4.2.1-0-g3de035335255 06/08/2016 JEMALLOC(3)
Helmut Schellong (04.06.2020, 15:04)
On 06/04/2020 14:11, Thomas Koenig wrote:
> Helmut Schellong <rip> schrieb:
> Ohne Erklärung, was das jeweils tut, ist dein Artikel relativ
> inhaltslos.


Stefan Reuther (04.06.2020, 18:44)
Am 03.06.2020 um 18:54 schrieb Thomas Koenig:
> Auf modernen 64-Bit-Systemen mit virtuellem Speicher funktioniert
> normalerweise jedes malloc() und liefert einen Pointer auf einen
> Speicherbereich zurück. Wenn man den Speicher dann wirklich
> verwenden möchte und der dann dank memory overcommitment dann doch
> nicht wirklich da ist, wundert man sich über ein einfrierendes
> System, einen Absturz oder dass irgendwas anderes abgeschossen
> wird...


Na dann schalt das Overcommitment doch aus?

> Gibt es da eigentlich Implementierungen von malloc, denen man eine
> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?


Im Zweifelsfall halt ein geeignetes ulimit.

Stefan
Thomas Koenig (04.06.2020, 20:37)
Stefan Reuther <stefan.news> schrieb:
> Am 03.06.2020 um 18:54 schrieb Thomas Koenig:
> Na dann schalt das Overcommitment doch aus?


Das ist nicht immer zielführend.

Beispiel: Man rechnet auf einem Knoten eines Supercomputers,
und wenn man für länger als ein paar Sekunden zu viel Speicher
braucht, dann wird der Prozess abgeschossen. Das macht ein
populäres Queing-System tatsächlich so.

>> Gibt es da eigentlich Implementierungen von malloc, denen man eine
>> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
>> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?

> Im Zweifelsfall halt ein geeignetes ulimit.


Dazu habe ich was interessantes festgestellt. Auf einem modernen
Linux scheint sich das, was man in der bash mit ulimit einstellt, nicht
zu vererben:

$ ulimit -m 10000
$ cat rlimit.c
#include <stdio.h>
#include <sys/time.h>
#include <sys/resource.h>

int main()
{
struct rlimit r;

getrlimit (RLIMIT_AS, &r);
printf ("rlim_cur = %ld, rlim_max = %ld\n", (unsigned long) r.rlim_cur,
(unsigned long) r.rlim_max);
return 0;
}
$ gcc rlimit.c
$ ./a.out
rlim_cur = -1, rlim_max = -1
$ ulimit -a | grep "max memory"
max memory size (kbytes, -m) 10000
$

aber:

$ prlimit --as=10000000 ./a.out
rlim_cur = 10000000, rlim_max = 10000000

Wee Tee Eff?
Christian Weisgerber (04.06.2020, 22:44)
On 2020-06-04, Thomas Koenig <tkoenig> wrote:

> Dazu habe ich was interessantes festgestellt. Auf einem modernen
> Linux scheint sich das, was man in der bash mit ulimit einstellt, nicht
> zu vererben:


RLIMIT_RSS: ulimit -m
RLIMIT_AS: ulimit -v
Enrik Berkhan (04.06.2020, 23:15)
Thomas Koenig <tkoenig> wrote:
> $ gcc rlimit.c
> $ ./a.out
> rlim_cur = -1, rlim_max = -1
> $ ulimit -a | grep "max memory"
> max memory size (kbytes, -m) 10000
> $
> aber:
> $ prlimit --as=10000000 ./a.out
> rlim_cur = 10000000, rlim_max = 10000000
> Wee Tee Eff?


max memory -> RLIMIT_RSS (unter Linux obsolet)

probier mal 'ulimit -v'

Viele Grüße,
Enrik
Florian Weimer (05.06.2020, 22:31)
* Christian Weisgerber:

> On 2020-06-03, Thomas Koenig <tkoenig> wrote:
>> Gibt es da eigentlich Implementierungen von malloc, denen man eine
>> Obergrenze mitgeben kann, also sowas wie "Rücke maximal $OBERGRENZE
>> Bytes raus, wenn es mehr werden, gib gefälligst NULL zurück"?

> Auf OpenBSD begrenzt RLIMIT_DATA auch wirkungsvoll malloc(3).


Auch auf Linux funktioniert das mittlerweile. Lange Zeit galt es dort
nur für brk (und war daher bei gängigen mallocs mit mmap-Fallback de
facto wirkungslos), inzwischen auch für mmap.

RLIMIT_RSS macht noch immer nichts unter Linux.

Daneben gibt es auch noch cgroups, die wiederum andere Auswirkungen
haben.
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