Voir :

• Supervision - sonde Nagios - Memoire Linux
• https://linuxblog.io/free-vs-available-memory-in-linux/
• https://en.pingcap.com/blog/linux-kernel-vs-memory-fragmentation-2/
• https://blog.stephane-robert.info/docs/admin-serveurs/linux/exploiter/memoire/
• /proc/sys/vm/compact_memory
• procmap
• pmap
• lsmem / chmem
• https://linuxfr.org/news/sortie-du-noyau-linux-6-17 damon_stat
• slabtop
• memstrack
• smem - memory reporting tool
• smemcap - data collection tool for memory reporting
• smemstat - memory usage monitoring tool
• SLAB / SLUB / SLOB

Linux Memory Management :

• https://lambdafunc.medium.com/linux-memory-management-2c13b5e386f1
• https://zedas.fr/posts/linux-explained-7-memory-management/
• https://www.abhik.ai/concepts/systems/memory-management
• Vidéo - The Linux Foundation - Introduction à la gestion de la mémoire sous Linux
• http://shtroumbiniouf.free.fr/CoursInfo/Systeme2/Cours/GestionMemoire/PageFault/PageFault.html
• https://www.youtube.com/watch?v=Gpm2-ktMLWs
• https://www.youtube.com/watch?v=A9WLYbE0p-I
• https://docs.kernel.org/mm/page_tables.html

Exemples :

• http://shtroumbiniouf.free.fr/CoursInfo/Systeme2/Cours/GestionMemoire/PageFault/PageFault.html#DebutPage

Voir :

• Valgrind
• https://www.hebergementwebs.com/tutoriels/linux-recherche-de-fuites-de-memoire-dans-les-programmes
• https://qastack.fr/unix/36450/how-can-i-find-a-memory-leak-of-a-running-process
• https://www.linuxtricks.fr/wiki/performance-memoire-avec-free-et-vmstat
• http://www.ordinateur.cc/syst%C3%A8mes/Linux/205699.html
• Atop - Case study with atop: memory leakage
• https://github.com/iovisor/bcc/blob/master/README.md tools/memleak

Voir :

• What is NUMA ?
• La mémoire : numactl, lstopo, perf, etc.
• numatop

Disable NUMA (Pour Oracle DB) /usr/share/doc/kernel-doc-4.18.0/Documentation/x86/x86_64/boot-options.txt

numa=off      Only set up a single NUMA node spanning all memory.

Vérif

numactl command can be used to check the status of NUMA

# numactl -H | grep available
available: 8 nodes (0-7)

# numactl -H | grep available
available: 2 nodes (0-1)

If the number of available nodes is 2 nodes (0-1) or 8 nodes (0-7) then NUMA is enabled

If the number of available nodes is 1 nodes (0) then NUMA is not enabled.

Voir aussi :

• numastat
• numademo

To identify NUMA nodes, socket memory and CPU core allocation

numactl -H

To identify the NUMA node local to an adapter

cat /sys/class/net/<interface>/device/numa_node

To identify memory allocation and use on a particular NUMA node:

cat /sys/devices/system/node/node<N>/numastat

To identify NUMA node mapping to cores, use one of the following

numactl --hardware
cat /sys/devices/system/node/node<N>/cpulist

Driver Loading - NUMA Node

numactl --cpunodebind=1 onload_tool reload

smem -u

Voir

• https://blog.zwindler.fr/2020/02/24/transparent-hugepages-mesurer-limpact-sur-les-performances/
• https://www.postgresql.org/docs/9.4/kernel-resources.html

cat /sys/kernel/mm/transparent_hugepage/enabled

The following is a sample output that shows Transparent HugePages are being used as the [always] flag is enabled.

[always] never

Paramètre Kernel Linux

transparent_hugepage=never

$ ./centreon_plugins.pl --plugin os::linux::snmp::plugin --mode memory --hostname localhost --help
...
    --patch-redhat
            If using Red Hat distribution with net-snmp >= 5.7.2-43 and
            net-snmp < 5.7.2-47. But you should update net-snmp!!!!

            This version: used = memTotalReal - memAvailReal // free =
            memAvailReal

            Others versions: used = memTotalReal - memAvailReal - memBuffer
            - memCached // free = total - used

free -mt
vmstat -SM 45 10
vmstat -SM -a 45 10
ps -C apache2 -o rss --no-headers | tr "\n" "+" | sed -e 's/+$/\n/' | bc
ps -e -o pid,user,%mem,rss,vsize,cmd --sort rss
ps -e -o pid,user,%mem,rss,vsize,cmd --sort vsize
ps -u $USER -o comm,vsz,pcpu | sort -nrk2
ps -eo comm,pcpu,pmem,rss --sort rss | tail -n 30 | tac

read CommitLimit Committed_AS <<< $(egrep "CommitLimit|Committed_AS" /proc/meminfo | awk '{print $2}')
echo $(( Committed_AS * 100 / CommitLimit))

memused=$(free  | grep "buffers/cache" | awk '{print $3}')
memtotal=$(free | grep ^Mem | awk '{print $2}')
echo $(( memused * 100 / memtotal))

memFree=$(free | grep ^- | awk '{print $3}')
memTot=$(free | grep ^Mem | awk '{print $2}')
memUsed=$(echo "scale=2 ; 100 * $memFree / $memTot" | bc)
echo "$memUsed %  Mem used" | grep ^[3-9][0-9]

ps -C apache2 -o rss --no-headers | tr "\n" "+" | sed -e 's/+$/\n/' | bc
read CommitLimit Committed_AS <<< $(egrep "CommitLimit|Committed_AS" /proc/meminfo | awk '{print $2}')
echo $(( Committed_AS * 100 / CommitLimit))
memused=$(free  | grep "buffers/cache" | awk '{print $3}')
memtotal=$(free | grep ^Mem | awk '{print $2}')
echo $(( memused * 100 / memtotal))
ps -e -o pid,user,rss,vsize,cmd --sort rss

smem -u
smem -u -t -k
top -b -n 1 -u apache

Taille totale de la mémoire physique de la RAM (sans la swap)

# head -1 /proc/meminfo
MemTotal:       65391036 kB

# awk '/MemTotal/ { print $2 }' /proc/meminfo
65391036

Voir : OOM Killer et Overcommit Memory http://www.blog.florian-bogey.fr/empecher-les-depassements-de-memoire-sur-un-serveur-linux.html

Clearing KernelCare Cache

Source : https://www.linuxjournal.com/content/how-install-and-uninstall-kernelcare

rm -rf /var/cache/kcare/patches
echo 1 > /proc/sys/vm/compact_memory
echo 3 > /proc/sys/vm/drop_caches
kcarectl –update

• https://www.postgresql.org/docs/current/kernel-resources.html Overcommit Memory Overcommit Accounting

Voir :

• https://clickhouse.com/blog/strict-memory-overcommit-for-postgres

vm.overcommit_memory=0 Default Heuristic overcommit handling

vm.overcommit_memory=1 Always overcommit. Appropriate for some scientific applications. Classic example is code using sparse arrays and just relying on the virtual memory consisting almost entirely of zero pages.

vm.overcommit_memory=2 Strict setting vm.overcommit_memory=2 DOES allow overcommit. If you set overcommit_ratio to (say) 200, then memory can be committed to the extent of swap +(RAM * 200/100).

The current overcommit limit and amount committed are viewable in /proc/meminfo as CommitLimit and Committed_AS

A la place de overcommit_ratio Il est possible d'utiliser vm.overcommit_kbytes

OOM echo -1000 > /proc/self/oom_score_adj

cat /proc/<pid>/oom_score echo -1000 > /proc/<pid>/oom_score_adj # protect from OOM kill

Or in a specific cgroup, set oom_kill_disable to 1.

echo 1000 > /proc/<pid>/oom_score_adj # mark as first target

===== For systemd services, use OOMScoreAdjust=-1000 in the unit file to protect critical processes. cgroup_enable=memory swapaccount=1 $ echo $¹⁾ MB 11389 MB $ cat /sys/fs/cgroup/memory/memory.stat

OOM is not invoked when memory.high is reached. However, if cgroup memory.max is reached then OOM is invoked. TLB hit TLB miss

sudo perf stat -e dTLB-loads,dTLB-load-misses,iTLB-loads,iTLB-load-misses -a sleep 60

perf list | grep -i tlb Slub

slabtop --sort=1

slabinfo -v access.redhat.com/ page_owner=on Premature swapping while there is still plenty of pagecache to be reclaimed Cgroup v1 https://access.redhat.com/solutions/6785021

https://fatdba.com/2025/12/12/when-linux-swaps-away-my-sleep-mysql-rhel8-and-the-curious-case-of-high-swap-usage/

https://docs.couchbase.com/server/current/install/install-swap-space.html

https://support.axway.com/kb/192440/language/en

https://communities.sas.com/t5/Administration-and-Deployment/Red-Hat-RHEL-8-Release-Swappiness-Algorithm-Setting-Requires/td-p/921008

https://docs.acceldata.io/odp/documentation/troubleshooting-premature-swapping

Change in swap behavior between RHEL 7 and RHEL 8 kernels https://access.redhat.com/solutions/7042476