linux-kernel - Re: [RFC PATCH -v2] mm, oom: introduce oom reaper

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Message-Id: <201511281339.JHH78172.SLOQFOFHVFOMJt@I-love.SAKURA.ne.jp>
Date:	Sat, 28 Nov 2015 13:39:11 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	mhocko@...nel.org, linux-mm@...ck.org
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	mgorman@...e.de, rientjes@...gle.com, riel@...hat.com,
	hughd@...gle.com, oleg@...hat.com, andrea@...nel.org,
	linux-kernel@...r.kernel.org, mhocko@...e.com
Subject: Re: [RFC PATCH -v2] mm, oom: introduce oom reaper

Michal Hocko wrote:
> for write while write but the probability is reduced considerably wrt.

Is this "while write" garbage?

> Users of mmap_sem which need it for write should be carefully reviewed
> to use _killable waiting as much as possible and reduce allocations
> requests done with the lock held to absolute minimum to reduce the risk
> even further.

It will be nice if we can have down_write_killable()/down_read_killable().

> The API between oom killer and oom reaper is quite trivial. wake_oom_reaper
> updates mm_to_reap with cmpxchg to guarantee only NUll->mm transition

NULL->mm

> and oom_reaper clear this atomically once it is done with the work.

Can't oom_reaper() become as compact as below?

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 3f22efc..c2ab7f9 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -472,21 +472,10 @@ static void oom_reap_vmas(struct mm_struct *mm)
 
 static int oom_reaper(void *unused)
 {
-	DEFINE_WAIT(wait);
-
 	while (true) {
-		struct mm_struct *mm;
-
-		prepare_to_wait(&oom_reaper_wait, &wait, TASK_UNINTERRUPTIBLE);
-		mm = READ_ONCE(mm_to_reap);
-		if (!mm) {
-			freezable_schedule();
-			finish_wait(&oom_reaper_wait, &wait);
-		} else {
-			finish_wait(&oom_reaper_wait, &wait);
-			oom_reap_vmas(mm);
-			WRITE_ONCE(mm_to_reap, NULL);
-		}
+		wait_event_freezable(oom_reaper_wait, mm_to_reap);
+		oom_reap_vmas(mm_to_reap);
+		mm_to_reap = NULL;
 	}
 
 	return 0;
--
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