OOM Killer 簡短筆記
緣由
滑 hacker news 時被 Out-of-memory victim selection with BPF 砸到，忽然有點好奇 OOM Killer Source Code。
Source Code
https://elixir.bootlin.com/linux/v6.6/source/mm/oom_kill.c#L192
c
/**
* oom_badness - heuristic function to determine which candidate task to kill
* @p: task struct of which task we should calculate
* @totalpages: total present RAM allowed for page allocation
*
* The heuristic for determining which task to kill is made to be as simple and
* predictable as possible. The goal is to return the highest value for the
* task consuming the most memory to avoid subsequent oom failures.
*/
long oom_badness(struct task_struct *p, unsigned long totalpages)
{
long points;
long adj;
if (oom_unkillable_task(p))
return LONG_MIN;
p = find_lock_task_mm(p);
if (!p)
return LONG_MIN;
/*
* Do not even consider tasks which are explicitly marked oom
* unkillable or have been already oom reaped or the are in
* the middle of vfork
*/
adj = (long)p->signal->oom_score_adj;
if (adj == OOM_SCORE_ADJ_MIN || test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
in_vfork(p)) {
task_unlock(p);
return LONG_MIN;
}
/*
* The baseline for the badness score is the proportion of RAM that each
* task's rss, pagetable and swap space use.
*/
points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
mm_pgtables_bytes(p->mm) / PAGE_SIZE;
task_unlock(p);
/* Normalize to oom_score_adj units */
adj *= totalpages / 1000;
points += adj;
return points;
}首先會排除以下 process：
kthread
正在 vfork
已經被 oom kill
被標記 oom skip
然後根據佔用記憶體（rss, swap, page）計算一個分數，越大越需要被 oom kill。
References
How does the OOM killer decide which process to kill first?
Out-of-memory victim selection with BPF
https://elixir.bootlin.com/linux/v6.6/source/mm/oom_kill.c#L192