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

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Date:	Wed, 27 Jun 2012 12:48:41 -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 Wed, 27 Jun 2012, Glauber Costa wrote:

> > @@ -2206,7 +2214,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup
> > *memcg, gfp_t gfp_mask,
> > >  	 * unlikely to succeed so close to the limit, and we fall back
> > >  	 * to regular pages anyway in case of failure.
> > >  	 */
> > > -	if (nr_pages == 1 && ret)
> > > +	if (nr_pages <= NR_PAGES_TO_RETRY && ret)
> > >  		return CHARGE_RETRY;
> 
> Changed to costly order.
> 

1 << PAGE_ALLOC_COSTLY_ORDER was the suggestion.

> One more thing. The original version of this patch included
> a cond_resched() here, that was also removed. From my re-reading
> of the code in page_alloc.c and vmscan.c now, I tend to think
> this is indeed not needed, since any cond_resched()s that might
> be needed to ensure the safety of the code will be properly
> inserted by the reclaim code itself, so there is no need for us
> to include any when we signal that a retry is needed.
> 

For __GFP_WAIT, that sounds like a safe guarantee.
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