Re: [PATCH] mm, oom_reaper: Move oom_lock from __oom_reap_task_mm()to oom_reap_task().

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> On Mon 12-12-16 12:59:18, Michal Hocko wrote:
> > On Mon 12-12-16 19:55:52, Tetsuo Handa wrote:
> > > Since commit 862e3073b3eed13f
> > > ("mm, oom: get rid of signal_struct::oom_victims")
> > > changed to wait until MMF_OOM_SKIP is set rather than wait while
> > > TIF_MEMDIE is set, rationale comment for commit e2fe14564d3316d1
> > > ("oom_reaper: close race with exiting task") needs to be updated.
> > 
> > True.
> > 
> > > While holding oom_lock can make sure that other threads waiting for
> > > oom_lock at __alloc_pages_may_oom() are given a chance to call
> > > get_page_from_freelist() after the OOM reaper called unmap_page_range()
> > > via __oom_reap_task_mm(), it can defer calling of __oom_reap_task_mm().
> > > 
> > > Therefore, this patch moves oom_lock from __oom_reap_task_mm() to
> > > oom_reap_task() (without any functional change). By doing so, the OOM
> > > killer can call __oom_reap_task_mm() if we don't want to defer calling
> > > of __oom_reap_task_mm() (e.g. when oom_evaluate_task() aborted by
> > > finding existing OOM victim's mm without MMF_OOM_SKIP).
> > 
> > But I fail to understand this part of the changelog. It sounds like a
> > preparatory for other changes. There doesn't seem to be any other user
> > of __oom_reap_task_mm in the current tree.

I'm planning to call __oom_reap_task_mm() from out_of_memory() if OOM
situation is not solved immediately, after we made sure that we give
enough CPU time to OOM killer and OOM reaper to run reclaim code by
mutex_lock_killable(&oom_lock) change.

> > 
> > Please send a patch which removes the comment which is no longer true
> > on its own and feel free to add
> > 
> > Acked-by: Michal Hocko <mhocko@suse.com>
> > 
> > but do not make other changes if you do not have any follow up patch
> > which would benefit from that.
> 
> Do you plan to pursue this?

Although I don't know whether we agree with mutex_lock_killable(&oom_lock)
change, I think this patch alone can go as a cleanup.

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