linux-kernel - Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

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Date:	Mon, 25 Jun 2012 16:33:29 -0700
From:	Suleiman Souhlal <suleiman@...gle.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	cgroups@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, devel@...nvz.org,
	kamezawa.hiroyu@...fujitsu.com, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

On Mon, Jun 25, 2012 at 7:15 AM, Glauber Costa <glommer@...allels.com> wrote:
> From: Suleiman Souhlal <ssouhlal@...eBSD.org>
>
> mem_cgroup_do_charge() was written before slab accounting, and expects
> three cases: being called for 1 page, being called for a stock of 32 pages,
> or being called for a hugepage.  If we call for 2 or 3 pages (and several
> slabs used in process creation are such, at least with the debug options I
> had), it assumed it's being called for stock and just retried without reclaiming.
>
> Fix that by passing down a minsize argument in addition to the csize.
>
> And what to do about that (csize == PAGE_SIZE && ret) retry?  If it's
> needed at all (and presumably is since it's there, perhaps to handle
> races), then it should be extended to more than PAGE_SIZE, yet how far?
> And should there be a retry count limit, of what?  For now retry up to
> COSTLY_ORDER (as page_alloc.c does), stay safe with a cond_resched(),
> and make sure not to do it if __GFP_NORETRY.

The commit description mentions COSTLY_ORDER, but it's not actually
used in the patch.

-- Suleiman
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