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Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying.

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On Sun 16-07-17 19:59:51, Tetsuo Handa wrote:
> Since the whole memory reclaim path has never been designed to handle the
> scheduling priority inversions, those locations which are assuming that
> execution of some code path shall eventually complete without using
> synchronization mechanisms can get stuck (livelock) due to scheduling
> priority inversions, for CPU time is not guaranteed to be yielded to some
> thread doing such code path.
> 
> mutex_trylock() in __alloc_pages_may_oom() (waiting for oom_lock) and
> schedule_timeout_killable(1) in out_of_memory() (already held oom_lock) is
> one of such locations, and it was demonstrated using artificial stressing
> that the system gets stuck effectively forever because SCHED_IDLE priority
> thread is unable to resume execution at schedule_timeout_killable(1) if
> a lot of !SCHED_IDLE priority threads are wasting CPU time [1].

I do not understand this. All the contending tasks will go and sleep for
1s. How can they preempt the lock holder?
-- 
Michal Hocko
SUSE Labs

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[PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-07-16 13:10 +0200
  Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Michal Hocko <mhocko@kernel.org> - 2017-07-17 11:00 +0200
    Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-07-17 16:00 +0200
      Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Michal Hocko <mhocko@kernel.org> - 2017-07-17 17:20 +0200
  Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Michal Hocko <mhocko@kernel.org> - 2017-07-17 17:30 +0200
    Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> - 2017-07-17 23:50 +0200
      Re: [PATCH v2] mm/page_alloc: Wait for oom_lock before retrying. Michal Hocko <mhocko@kernel.org> - 2017-07-18 11:10 +0200

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