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Ci-dessous, les différences entre deux révisions de la page.

--- tech:notes_swap_memoire [2025/03/24 15:06] – créée - modification externe 127.0.0.1
+++ tech:notes_swap_memoire [2026/07/20 09:51] (Version actuelle) – Jean-Baptiste
@@ Ligne 1: / Ligne 1: @@
+<!DOCTYPE markdown>
+{{tag>Brouillon Mémoire SWAP Kernel Linux}}
+# Notes swap mémoire
+Voir :
+* https://wiki.debian.org/Swap
+* https://chrisdown.name/2018/01/02/in-defence-of-swap.html
+* https://kubernetes.io/blog/2025/03/25/swap-linux-improvements/
+Voir aussi :
+* [[Swap sur ramdisk]]
+~~~bash
+systemctl --type swap
+cat /proc/swaps
+cat /proc/vmstat
+~~~
+~~~bash
+echo 0 > /proc/sys/vm/swappiness
+# cat /proc/sys/vm/vfs_cache_pressure
+# sysctl -w vm.vfs_cache_pressure=50
+~~~
+~~~bash
+# 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
+~~~bash
+smem -u -s swap
+~~~
+Consommation de la SWAP par process
+~~~bash
+smem -s swap
+~~~
+ou
+~~~bash
+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
+~~~
+ou
+~~~bash
+for file in /proc/*/status ; do awk '/Tgid|VmSwap|Name/{printf $2 " " $3}END{ print ""}' $file; done | grep kB | sort -k 3 -n
+~~~
+## dphys-swapfile
+~~~bash
+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 :
+* https://en.wikipedia.org/wiki/Memory_paging
+* https://www.reddit.com/r/linux4noobs/comments/1aep2bc/why_is_swap_used_when_there_is_ram_available/
+Voir aussi :
+* Shared Memory
+* zramctl
+~~~bash
+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
+~~~
+Voir VmSwap ou VmSize
+~~~bash
+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
+~~~
+## Tests SWAP
+Utiliser 2 giga de mémoire
+~~~bash
+stress --vm 1 --vm-bytes 2G --timeout 30
+~~~
+Vérif
+~~~bash
+journalctl -k | grep -i "out of memory"
+~~~
+Autres test
+~~~c
+#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