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

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Date:	Tue, 26 Jun 2012 02:17:45 -0700 (PDT)
From:	David Rientjes <rientjes@...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>,
	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>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

On Tue, 26 Jun 2012, Glauber Costa wrote:

> > Nope, have you checked the output of /sys/kernel/slab/.../order when
> > running slub?  On my workstation 127 out of 316 caches have order-2 or
> > higher by default.
> > 
> 
> Well, this is still on the side of my argument, since this is still a majority
> of them being low ordered.

Ok, so what happens if I pass slub_min_order=2 on the command line?  We 
never retry?

> The code here does not necessarily have to retry -
> if I understand it correctly - we just retry for very small allocations
> because that is where our likelihood of succeeding is.
> 

Well, the comment for NR_PAGES_TO_RETRY says

	/*
	 * We need a number that is small enough to be likely to have been
	 * reclaimed even under pressure, but not too big to trigger unnecessary 
	 * retries
	 */

and mmzone.h says

	/*
	 * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed
	 * costly to service.  That is between allocation orders which should
	 * coalesce naturally under reasonable reclaim pressure and those which
	 * will not.
	 */
	#define PAGE_ALLOC_COSTLY_ORDER 3

so I'm trying to reconcile which one is correct.
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