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Date: Wed, 13 Jan 2016 16:57:08 -0800 (PST) From: David Rientjes <rientjes@...gle.com> To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp> cc: mhocko@...nel.org, hannes@...xchg.org, akpm@...ux-foundation.org, mgorman@...e.de, torvalds@...ux-foundation.org, oleg@...hat.com, hughd@...gle.com, andrea@...nel.org, riel@...hat.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] mm,oom: Exclude TIF_MEMDIE processes from candidates. On Wed, 13 Jan 2016, Tetsuo Handa wrote: > David Rientjes wrote: > > > @@ -171,7 +195,7 @@ unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg, > > > if (oom_unkillable_task(p, memcg, nodemask)) > > > return 0; > > > > > > - p = find_lock_task_mm(p); > > > + p = find_lock_non_victim_task_mm(p); > > > if (!p) > > > return 0; > > > > > > > I understand how this may make your test case pass, but I simply don't > > understand how this could possibly be the correct thing to do. This would > > cause oom_badness() to return 0 for any process where a thread has > > TIF_MEMDIE set. If the oom killer is called from the page allocator, > > kills a thread, and it is recalled before that thread may exit, then this > > will panic the system if there are no other eligible processes to kill. > > > Why? oom_badness() is called after oom_scan_process_thread() returned OOM_SCAN_OK. > oom_scan_process_thread() returns OOM_SCAN_ABORT if a thread has TIF_MEMDIE set. > oom_scan_process_thread() checks for TIF_MEMDIE on p, not on p's threads. If one of p's threads has TIF_MEMDIE set and p does not, we actually want to set TIF_MEMDIE for p. That's the current behavior since it will lead to p->mm memory freeing. Your patch is excluding such processes entirely and selecting another process to kill unnecessarily.
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