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--- doc:appunti:linux:sa:linux_virtual_memory [2023/12/18 11:21] – niccolo
+++ doc:appunti:linux:sa:linux_virtual_memory [2023/12/18 12:42] (current) – [Come rilasciare la cache] niccolo
@@ Line 1: / Line 1: @@
 ====== Linux Virtual Memory ======
+===== Diagnosi di Out of Memory Killer =====
+Come diagnosticare problemi //Out of Memory Killer//? Nel syslog si legge quanto segue:
+<code>
+kernel: apache2 invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE),
+        order=0, oom_score_adj=0
+...
+kernel: Mem-Info:
+kernel: active_anon:31868 inactive_anon:3867772 isolated_anon:0
+kernel:  active_file:196 inactive_file:169 isolated_file:0
+kernel:  unevictable:3724 dirty:0 writeback:0
+kernel:  slab_reclaimable:8784 slab_unreclaimable:23394
+kernel:  mapped:32570 shmem:33575 pagetables:16400 bounce:0
+kernel:  free:33008 free_pcp:981 free_cma:0
+...
+kernel: Tasks state (memory values in pages):
+kernel: [  pid  ]   uid  tgid total_vm      rss pgtables_bytes swapents oom_score_adj name
+kernel: [    279]     0   279    54600      891   462848        0          -250 systemd-journal
+...
+kernel: [2109336]    33 2109336    77411    14582   282624        0             0 apache2
+kernel: [2109339]    33 2109339    76387    14063   274432        0             0 apache2
+kernel: [2109340]    33 2109340    75360    12557   262144        0             0 apache2
+...
+kernel: Out of memory: Killed process 1102 (mariadbd) total-vm:2663252kB, anon-rss:429744kB,
+        file-rss:0kB, shmem-rss:0kB, UID:106 pgtables:1172kB oom_score_adj:0
+</code>
+Quindi una richiesta di allocazione memoria da parte del processo **apache2** ha causato il kill del processo **mariadbd**. Anche l'elenco dei processi //Tasks state// evidenzia la presenza di **151 processi** apache2.
 <code>
@@ Line 20: / Line 51: @@
 ^ Active(file)  | The amount of file cache memory, in kibibytes, that is in active use, or was in active use since the last time the system reclaimed memory.  |
+===== Come rilasciare la cache =====
+Per rilasciare le **PageCache** si può usare il comando:
+<code>
+sync; echo 1 > /proc/sys/vm/drop_caches
+</code>
+Dovrebbero andare a zero diversi contatori, tra cui quello della **Active** memory.
+Il parametro **1** scritto nello pseudofile può assumere valori diversi, a seconda di cosa si voglia rilasciare:
+^ 1  | Clears only the page cache.  |
+^ 2  | Clears dentries and inodes.  |
+^ 3  | Clears page cache, dentries, and inodes.  |
 ===== Web References =====
@@ Line 26: / Line 71: @@
   * **[[https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/deployment_guide/s2-proc-meminfo|/proc/meminfo]]**
   * **[[https://access.redhat.com/solutions/406773|Interpreting /proc/meminfo and free output for Red Hat Enterprise Linux]]**
+  * **[[https://www.tecmint.com/clear-ram-memory-cache-buffer-and-swap-space-on-linux/|How to Clear RAM Memory Cache, Buffer and Swap Space on Linux]]**