linux-kernel - Re: [PATCH V5] Allow compaction of unevictable pages

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Message-ID: <20150313190915.GA12589@akamai.com>
Date:	Fri, 13 Mar 2015 15:09:15 -0400
From:	Eric B Munson <emunson@...mai.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5] Allow compaction of unevictable pages

On Fri, 13 Mar 2015, Rik van Riel wrote:

> On 03/13/2015 01:26 PM, Eric B Munson wrote:
> 
> > --- a/mm/compaction.c
> > +++ b/mm/compaction.c
> > @@ -1046,6 +1046,8 @@ typedef enum {
> >  	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
> >  } isolate_migrate_t;
> >  
> > +int sysctl_compact_unevictable;
> > +
> >  /*
> >   * Isolate all pages that can be migrated from the first suitable block,
> >   * starting at the block pointed to by the migrate scanner pfn within
> 
> I suspect that the use cases where users absolutely do not want
> unevictable pages migrated are special cases, and it may make
> sense to enable sysctl_compact_unevictable by default.

Given that sysctl_compact_unevictable=0 is the way the kernel behaves
now and the push back against always enabling compaction on unevictable
pages, I left the default to be the behavior as it is today.  I agree
that this is likely the minority case, but I'd really like Peter Z or
someone else from real time to say that they are okay with the default
changing.

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