Re: [PATCH 4/9] mm: oom_kill: generalize OOM progress waitqueue
From: David Rientjes
Date: Tue Apr 28 2015 - 18:40:15 EST
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@xxxxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
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