linux-kernel - Re: [PATCH v2 5/9] mm/compaction: allow to scan nonmovable pageblock when depleted state

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Date:	Wed, 30 Sep 2015 17:30:23 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v2 5/9] mm/compaction: allow to scan nonmovable pageblock
 when depleted state

On Fri, Sep 25, 2015 at 12:32:02PM +0200, Vlastimil Babka wrote:
> On 08/24/2015 04:19 AM, Joonsoo Kim wrote:
> 
> [...]
> 
> > 
> > Because we just allow freepage scanner to scan non-movable pageblock
> > in very limited situation, more scanning events happen. But, allowing
> > in very limited situation results in a very important benefit that
> > memory isn't fragmented more than before. Fragmentation effect is
> > measured on following patch so please refer it.
> 
> AFAICS it's measured only for the whole series in the cover letter, no? Just to
> be sure I didn't overlook something.

It takes too much time so no measurement is done on every patch.
I will try to measure it on at least this patch in next revision.

> 
> > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> > ---
> >  include/linux/mmzone.h |  1 +
> >  mm/compaction.c        | 27 +++++++++++++++++++++++++--
> >  2 files changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index e13b732..5cae0ad 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -545,6 +545,7 @@ enum zone_flags {
> >  					 */
> >  	ZONE_FAIR_DEPLETED,		/* fair zone policy batch depleted */
> >  	ZONE_COMPACTION_DEPLETED,	/* compaction possiblity depleted */
> > +	ZONE_COMPACTION_SCANALLFREE,	/* scan all kinds of pageblocks */
> 
> "SCANALLFREE" is hard to read. Otherwise yeah, I agree scanning unmovable
> pageblocks is necessary sometimes, and this seems to make a reasonable tradeoff.

Good! I will think better name.

Thanks.

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