linux-kernel - Re: [patch] mm, compaction: abort free scanner if split fails

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Date:	Wed, 22 Jun 2016 15:42:07 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Vlastimil Babka <vbabka@...e.cz>, Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Mel Gorman <mgorman@...hsingularity.net>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, stable@...r.kernel.org
Subject: Re: [patch] mm, compaction: abort free scanner if split fails

On Wed, 22 Jun 2016 15:06:29 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:

> On Wed, 22 Jun 2016, Andrew Morton wrote:
> 
> > On Tue, 21 Jun 2016 18:22:49 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:
> > 
> > > If the memory compaction free scanner cannot successfully split a free
> > > page (only possible due to per-zone low watermark), terminate the free 
> > > scanner rather than continuing to scan memory needlessly.  If the 
> > > watermark is insufficient for a free page of order <= cc->order, then 
> > > terminate the scanner since all future splits will also likely fail.
> > > 
> > > This prevents the compaction freeing scanner from scanning all memory on 
> > > very large zones (very noticeable for zones > 128GB, for instance) when 
> > > all splits will likely fail while holding zone->lock.
> > > 
> > 
> > This collides pretty heavily with Joonsoo's "mm/compaction: split
> > freepages without holding the zone lock".
> > 
> 
> Sorry if it wasn't clear, but I was proposing this patch for 4.7 
> inclusion and Vlastimil agreed we should ask for that.  Joonsoo said he 
> was prepared to rebase on top of that.  Is 
> mm-compaction-split-freepages-without-holding-the-zone-lock.patch and 
> friends going into 4.7 or are we deferring this fix until 4.8?

I have this patch lined up for 4.7 so I was rebasing Joonsoo's patches
on top.