Notes swap mémoire

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Swap sur ramdisk

systemctl --type swap
cat /proc/swaps
cat /proc/vmstat

echo 0 > /proc/sys/vm/swappiness
# cat /proc/sys/vm/vfs_cache_pressure
# sysctl -w vm.vfs_cache_pressure=50

# Allocate storage and restrict access
fallocate --length 4GiB /swapfile
chmod 600 /swapfile
 
# Format the swap space
mkswap /swapfile
 
# Activate the swap space for paging
swapon /swapfile

Analyse consommation

Consommation de la SWAP par utilisateur

smem -u -s swap

Consommation de la SWAP par process

smem -s swap

ou

echo -e "SWAP_KB\tPPID\tPID\tEXE"
 
for S_FILE in /proc/[0-9]*/ ; 
do 
  S_PPID="$(awk '/^PPid:/ { print $2}' ${S_FILE}/status)" ;
  S_PID="$(echo ${S_FILE}/status | cut -d'/' -f3)" ;  
  S_EXE="$(readlink $S_FILE/exe)" ; 
  S_SWAPKB="$(awk '/VmSwap/ { print $2}' ${S_FILE}/status)" ; 
  [ ! -z $S_SWAPKB ] && echo -e "$S_SWAPKB\t${S_PPID}\t${S_PID}\t${S_EXE}" ; 
done | sort -n

dphys-swapfile

dphys-swapfile swapoff

Recommandations SWAP

Prereq Oracle

RAM	Swap Space
Between 1 GB and 2 GB	1.5 times the size of the RAM
Between 2 GB and 16 GB	Equal to the size of the RAM
More than 16 GB	16GB
RAM	Swap Space
Between 8 GB and 16 GB	Equal to the size of the RAM
More than 16 GB	16GB

Recommandations RedHat

Source : https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_storage_devices/getting-started-with-swap_managing-storage-devices

Amount of RAM in the system	Recommended swap space	Recommended swap space if allowing for hibernation
⩽ 2 GB	2 times the amount of RAM	3 times the amount of RAM
> 2 GB – 8 GB	Equal to the amount of RAM	2 times the amount of RAM
> 8 GB – 64 GB	At least 4 GB	1.5 times the amount of RAM
> 64 GB	At least 4 GB	Hibernation not recommended

Utilisation de SWAP alors que la RAM n'est que partiellement utilisé

En anglais sur les forums :

Why is Swap used when there is RAM available?
Swap being used when RAM is almost half free
Why linux has enough memory but swap is used
Why is Linux not using RAM but only Swap ?
System suddenly using all available swap, but plenty of free memory
High swap usage in spite of low RAM usage

Voir :

Voir aussi :

Shared Memory
zramctl

cat /proc/meminfo

cat /proc/sys/vm/swappiness
cat /proc/sys/vm/dirty_ratio
cat /proc/sys/vm/dirty_background_ratio
cat /proc/sys/vm/overcommit_ratio

ps -eo pmem,pcpu,rss,vsize,args --sort rss
grep VmSwap /proc/*/status | sort -n -r --key=2.1 | head -5
grep Vm /proc/3593/status

#include <stdlib.h>
#include <strings.h>
#include <unistd.h>
 
int main()
{
    char *p;
    size_t s = 100 * 1024 * 1024;
 
    for (;;)
    {
        p = malloc(s);
        bzero(p, s);
        sleep(1);
    }
 
    /* unreached */
}

Source : https://bbs.archlinux.org/viewtopic.php?id=212750