linux-kernel - Re: [PATCH 4/9] mm: oom_kill: generalize OOM progress waitqueue

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Message-ID: <alpine.DEB.2.10.1504281539520.10203@chino.kir.corp.google.com>
Date:	Tue, 28 Apr 2015 15:40:05 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Johannes Weiner <hannes@...xchg.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] mm: oom_kill: generalize OOM progress waitqueue

On Mon, 27 Apr 2015, Johannes Weiner wrote:

> It turns out that the mechanism to wait for exiting OOM victims is
> less generic than it looks: it won't issue wakeups unless the OOM
> killer is disabled.
> 
> The reason this check was added was the thought that, since only the
> OOM disabling code would wait on this queue, wakeup operations could
> be saved when that specific consumer is known to be absent.
> 
> However, this is quite the handgrenade.  Later attempts to reuse the
> waitqueue for other purposes will lead to completely unexpected bugs
> and the failure mode will appear seemingly illogical.  Generally,
> providers shouldn't make unnecessary assumptions about consumers.
> 
> This could have been replaced with waitqueue_active(), but it only
> saves a few instructions in one of the coldest paths in the kernel.
> Simply remove it.
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Acked-by: Michal Hocko <mhocko@...e.cz>

Acked-by: David Rientjes <rientjes@...gle.com>
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