Re: [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path

From: David Rientjes <rientjes@google.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Mikulas Patocka <mpatocka@redhat.com>,
	Ondrej Kozina <okozina@redhat.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Mel Gorman <mgorman@suse.de>, Neil Brown <neilb@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	dm-devel@redhat.com, Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH 1/2] mempool: do not consume memory reserves from the reclaim path
Date: Mon, 18 Jul 2016 19:00:57 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.10.1607181858020.16586@chino.kir.corp.google.com> (raw)
In-Reply-To: <1468831285-27242-1-git-send-email-mhocko@kernel.org>

On Mon, 18 Jul 2016, Michal Hocko wrote:

> David Rientjes was objecting that such an approach wouldn't help if the
> oom victim was blocked on a lock held by process doing mempool_alloc. This
> is very similar to other oom deadlock situations and we have oom_reaper
> to deal with them so it is reasonable to rely on the same mechanism
> rather inventing a different one which has negative side effects.
> 

Right, this causes oom livelock as described in the aforementioned thread: 
the oom victim is waiting on a mutex that is held by a thread doing 
mempool_alloc().  The oom reaper is not guaranteed to free any memory, so 
nothing on the system can allocate memory from the page allocator.

I think the better solution here is to allow mempool_alloc() users to set 
__GFP_NOMEMALLOC if they are in a context which allows them to deplete 
memory reserves.

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