watch -n 1 -d grep ^Commit /proc/meminfo
watch -n 1 -d free -m
ps -eo vsz,rss,pid,args | sed 1d | sort -n
sar -r
sar -S
vmstat 1
Program overcommit:
/*
*
* overcommit.c
*
* Allocate memory given the size in argument.
*
* Guillaume Kielwasser 2013/10/12
*
*/
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#define VERSION "0.1"
char *prog_name = NULL;
int usage ()
{
fprintf (stderr, "Usage: %s [-Vh] [-m] mem_Mb\n", prog_name);
exit (EXIT_FAILURE);
}
int main (int argc, char **argv)
{
int opt;
int V_FLAG = 0, H_FLAG = 0, M_FLAG = 0;
char *version = VERSION;
char *ptr = NULL;
size_t mem = 0;
unsigned long i = 0;
prog_name = argv[0];
while ((opt = getopt (argc, argv, "Vhm")) != -1) {
switch (opt) {
case 'V':
V_FLAG = 1;
break;
case 'h':
H_FLAG = 1;
break;
case 'm':
M_FLAG = 1;
break;
default:
usage ();
}
}
if (V_FLAG) {
printf ("%s version %s\n", prog_name, version);
return (EXIT_SUCCESS);
}
if (H_FLAG)
usage ();
if (argc != optind + 1)
usage ();
if ((mem = 1024*1024 * (size_t) atoi (argv[optind])) == 0) {
fprintf (stderr, "%s: %s not a number\n",
prog_name, argv[optind]);
exit (EXIT_FAILURE);
}
if ((ptr = (char *) malloc (mem)) == NULL) {
fprintf (stderr, "%s: malloc %lu failed (%s)\n",
prog_name, mem, strerror (errno));
exit (EXIT_FAILURE);
}
if (M_FLAG) {
for (i=0; i<mem; i++)
memset (ptr++, 0, 1);
}
while (1) {
sleep (1);
}
return (EXIT_SUCCESS);
}
Makefile:
CC = gcc
CFLAGS = -s -Wall -O3
overcommit: overcommit.c
$(CC) $(CFLAGS) -o overcommit overcommit.c
Set the overcommit_memory tunable to 0:
sysctl -w vm.overcommit_memory=0
Obvious overcommits of address space are refused. Allows overcommit to reduce swap usage. This feature can be very useful because there are a lot of programs that malloc() huge amounts of memory "just-in-case" and don't use much of it.
Example on a system with 2Gb of RAM and 2Gb of swap:
$ grep -E 'MemTotal:|SwapTotal:' /proc/meminfo MemTotal: 1986160 kB SwapTotal: 2030588 kB
asking 3Gb of memory works:
$ ./overcommit 3000
but asking for 3.5Gb is not permitted (considered here as obvious overcommit):
$ ./overcommit 3500 ./overcommit: malloc 3670016000 failed (Cannot allocate memory)
FYI: /proc/meminfo CommitLimit has nothing to do with the obvious limit calculation; it only servers in "never overcommit" mode.
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1148268 kB
$ free -m
total used free shared buffers cached
Mem: 1939 821 1118 0 55 419
-/+ buffers/cache: 345 1593
Swap: 1982 16 1966
./overcommit -m 1000
$ ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 1028160 1024404 6728 ./overcommit -m 1000
$ grep ^Commit /proc/meminfo
CommitLimit: 3023668 kB
Committed_AS: 2170544 kB
$ free -m
total used free shared buffers cached
Mem: 1939 1823 116 0 56 419
-/+ buffers/cache: 1347 592
Swap: 1982 16 1966
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1145828 kB
$ free -m
total used free shared buffers cached
Mem: 1939 821 1117 0 56 419
-/+ buffers/cache: 345 1594
Swap: 1982 16 1966
./overcommit 1000
$ ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 1028160 356 7380 ./overcommit 1000
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 2170132 kB
$ free -m
total used free shared buffers cached
Mem: 1939 821 1117 0 56 419
-/+ buffers/cache: 345 1594
Swap: 1982 16 1966
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1143952 kB
$ free -m
total used free shared buffers cached
Mem: 1939 830 1109 0 57 420
-/+ buffers/cache: 352 1587
Swap: 1982 16 1966
./overcommit 2900 &
./overcommit 2900 &
./overcommit 2900 &
$ ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 2973760 356 7941 ./overcommit 2900 2973760 356 7942 ./overcommit 2900 2973760 356 7943 ./overcommit 2900
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 10053432 kB
total used free shared buffers cached
Mem: 1939 830 1109 0 57 420
-/+ buffers/cache: 352 1587
Swap: 1982 16 1966
$ sar -r 14:02:01 kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact 14:03:01 1135508 850652 42,83 58984 430348 1145256 28,51 362912 364516 14:04:01 1134036 852124 42,90 59032 430412 1145320 28,51 364476 364584 14:05:01 1134460 851700 42,88 59108 430292 1145192 28,51 364272 364772 14:06:01 1135304 850856 42,84 59196 430292 10054664 250,32 363160 364884 14:07:01 1134660 851500 42,87 59256 430312 10054680 250,32 363236 364980 14:08:01 1137496 848664 42,73 59360 430296 10054600 250,32 360792 364796 Average: 1142628 843532 42,47 40850 300155 1811622 45,10 361707 352409
$ free -m
total used free shared buffers cached
Mem: 1939 581 1358 0 4 68
-/+ buffers/cache: 509 1430
Swap: 1982 0 1982
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1444952 kB
./overcommit -m 3000
$ free -m
total used free shared buffers cached
Mem: 1939 1868 71 0 4 74
-/+ buffers/cache: 1789 150
Swap: 1982 1768 214
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 4497040 kB
./overcommit -m 2000
$ ./overcommit -m 3000 Killed
$ free -m
total used free shared buffers cached
Mem: 1939 1867 71 0 0 47
-/+ buffers/cache: 1819 120
Swap: 1982 801 1181
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 3473256 kB
Oct 13 18:04:24 voyager kernel: [158113.978944] Out of memory: Kill process 31659 (overcommit) score 766 or sacrifice child Oct 13 18:04:24 voyager kernel: [158113.978947] Killed process 31659 (overcommit) total-vm:3076160kB, anon-rss:1266632kB, file-rss:364kB
Set the overcommit_memory tunable to 1.
sysctl -w vm.overcommit_memory=1
When this flag is 1, the kernel pretends there is always enough memory until it actually runs out.
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1331804 kB
$ free -m
total used free shared buffers cached
Mem: 1939 575 1363 0 3 83
-/+ buffers/cache: 489 1450
Swap: 1982 0 1982
Let's allocate 95Tb of memory:
./overcommit 100000000
$ ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 102400004160 356 19884 ./overcommit 100000000
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 102401332116 kB
$ free -m
total used free shared buffers cached
Mem: 1939 576 1362 0 3 83
-/+ buffers/cache: 490 1449
Swap: 1982 0 1982
$ sar -r 21:00:02 kbmemfree kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact 21:01:02 1558000 428160 21.56 1480 63636 1341020 62.27 136816 172588 21:02:01 1402080 584080 29.41 2520 83792 1338016 33.31 164544 301580 21:03:01 1396800 589360 29.67 2552 88672 615741392 15329.35 165416 305964 21:04:01 1398452 587708 29.59 3312 84956 1333036 33.19 166904 302732 21:05:01 1396364 589796 29.70 3328 85044 1333036 33.19 169356 302828 21:06:01 1391520 594640 29.94 3644 86600 102401333260 2549359.16 172152 304568 21:07:01 1386324 599836 30.20 10256 100260 102401331020 2549359.11 162880 319300 21:08:01 1382360 603800 30.40 10448 100420 102401331660 2549359.12 166580 319156 Average: 537358 1448802 72.94 127415 279140 555181698 13821.67 797146 501741
Set the overcommit_memory tunable to 2.
sysctl -w vm.overcommit_memory=2
When this flag is 2, the kernel uses a "never overcommit" policy that attempts to prevent any overcommit of memory. When overcommit_memory is set to 2, the total committed address space of the system is not permitted to exceed swap plus the vm.overcommit_ratio percentage of physical RAM, ie, the CommitLimit of /proc/meminfo.
$ grep ^Commit /proc/meminfo CommitLimit: 3023668 kB Committed_AS: 1330612 kB
$ free -m
total used free shared buffers cached
Mem: 1939 594 1344 0 10 100
-/+ buffers/cache: 484 1455
Swap: 1982 0 1982
./overcommit 2000 ./overcommit: malloc 2097152000 failed (Cannot allocate memory)
As 1Gb of memory was already commited (Committed_AS), asking for 2 more Gb is not permitted (limit is CommitLimit).
The buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. The cache only contains the contents of the files themselves.
Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.
To free pagecache:
echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
echo 3 > /proc/sys/vm/drop_caches
As this is a non-destructive operation and dirty objects are not freeable, the
user should run `sync' first.
sync && echo 3 > /proc/sys/vm/drop_caches
$ free -m
total used free shared buffers cached
Mem: 1939 559 1380 0 0 81
-/+ buffers/cache: 477 1462
Swap: 1982 0 1982
find /usr -exec ls -l {} \; > /dev/null 2>&1$ free -m
total used free shared buffers cached
Mem: 1939 846 1092 0 147 92
-/+ buffers/cache: 606 1333
Swap: 1982 0 1982
$ free -m
total used free shared buffers cached
Mem: 1939 552 1386 0 0 77
-/+ buffers/cache: 474 1465
Swap: 1982 0 1982
dd if=/dev/sda of=/dev/null
$ free -m
total used free shared buffers cached
Mem: 1939 1806 133 0 1219 77
-/+ buffers/cache: 509 1430
Swap: 1982 0 1982
$ free -m
total used free shared buffers cached
Mem: 1939 557 1381 0 0 78
-/+ buffers/cache: 479 1460
Swap: 1982 0 1982
dd if=/dev/zero of=/tmp/dd.tmp bs=1024 count=1048576
$ free -m
total used free shared buffers cached
Mem: 1939 1619 319 0 2 1103
-/+ buffers/cache: 513 1425
Swap: 1982 0 1982
$ free -m
total used free shared buffers cached
Mem: 1939 553 1386 0 0 78
-/+ buffers/cache: 474 1465
Swap: 1982 0 1982
$ dd if=/tmp/dd.tmp of=/dev/null 2097152+0 records in 2097152+0 records out 1073741824 bytes (1.1 GB) copied, 31.8524 s, 33.7 MB/s
$ free -m
total used free shared buffers cached
Mem: 1939 1591 348 0 1 1111
-/+ buffers/cache: 477 1461
Swap: 1982 0 1982
$ dd if=/tmp/dd.tmp of=/dev/null 2097152+0 records in 2097152+0 records out 1073741824 bytes (1.1 GB) copied, 1.61037 s, 667 MB/s
from http://www.linuxhowtos.org/System/Linux Memory Management.htm
VIRT stands for the virtual size of a process, which is the sum of memory it is actually using, memory it has mapped into itself (for instance the video card's RAM for the X server), files on disk that have been mapped into it (most notably shared libraries), and memory shared with other processes. VIRT represents how much memory the program is able to access at the present moment. RES stands for the resident size, which is an accurate representation of how much actual physical memory a process is consuming. (This also corresponds directly to the %MEM column.) This will virtually always be less than the VIRT size, since most programs depend on the C library. SHR indicates how much of the VIRT size is actually sharable memory or libraries). In the case of libraries, it does not necessarily mean that the entire library is resident. For example, if a program only uses a few functions in a library, the whole library is mapped and will be counted in VIRT and SHR, but only the parts of the library file containing the functions being used will actually be loaded in and be counted under RES.
./overcommit 2000
$ ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 2052160 356 6179 ./overcommit 2000
$ grep ^Vm /proc/6179/status VmPeak: 2052160 kB VmSize: 2052160 kB VmLck: 0 kB VmPin: 0 kB VmHWM: 356 kB VmRSS: 356 kB VmData: 2048048 kB VmStk: 136 kB VmExe: 4 kB VmLib: 1884 kB VmPTE: 32 kB VmSwap: 0 kB
VmPeak peak virtual memory size
VmSize total program size
VmLck locked memory size
VmHWM peak resident set size ("high water mark")
VmRSS size of memory portions
VmData size of data, stack, and text segments
VmStk size of data, stack, and text segments
VmExe size of text segment
VmLib size of shared library code
VmPTE size of page table entries
VmSwap size of swap usage (the number of referred swapents)
./overcommit -m 1000
# ps -eo vsz,rss,pid,args | grep 'overcommi[t]' 1028160 1024404 6532 ./overcommit -m 1000
# grep ^Vm /proc/6532/status VmPeak: 1028160 kB VmSize: 1028160 kB VmLck: 0 kB VmPin: 0 kB VmHWM: 1024404 kB VmRSS: 1024404 kB VmData: 1024048 kB VmStk: 136 kB VmExe: 4 kB VmLib: 1884 kB VmPTE: 2028 kB VmSwap: 0 kB
stack.c:
#define SIZE 2147483648
main ()
{
char a[SIZE];
while (1) {
sleep (1);
}
}
gcc -o stack stack.c
ulimit -s unlimited
./stack
$ ps -eo vsz,rss,pid,args | grep 'stac[k]$' 2101176 348 16403 ./stack
$ grep ^Vm /proc/16403/status VmPeak: 2101176 kB VmSize: 2101176 kB VmLck: 0 kB VmPin: 0 kB VmHWM: 348 kB VmRSS: 348 kB VmData: 40 kB VmStk: 2097160 kB VmExe: 4 kB VmLib: 1884 kB VmPTE: 28 kB VmSwap: 0 kB