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= Notes swap mémoire

Voir :
* 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]]

<code bash>
systemctl --type swap
cat /proc/swaps
cat /proc/vmstat
</code>

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

<code 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
</code>


== Analyse consommation

Consommation de la SWAP par utilisateur
<code bash>
smem -u -s swap
</code>

Consommation de la SWAP par process
<code bash>
smem -s swap
</code>

ou
<code 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
</code>



== dphys-swapfile

<code bash>
dphys-swapfile swapoff 
</code>

== 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                        |