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

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Message-ID: <alpine.DEB.2.10.1607181858020.16586@chino.kir.corp.google.com>
Date:	Mon, 18 Jul 2016 19:00:57 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Michal Hocko <mhocko@...nel.org>
cc:	linux-mm@...ck.org, Mikulas Patocka <mpatocka@...hat.com>,
	Ondrej Kozina <okozina@...hat.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Mel Gorman <mgorman@...e.de>, Neil Brown <neilb@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, dm-devel@...hat.com,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [RFC PATCH 1/2] mempool: do not consume memory reserves from
 the reclaim path

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.