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

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Message-ID: <560522A2.50609@suse.cz>
Date:	Fri, 25 Sep 2015 12:32:02 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Joonsoo Kim <js1304@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	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>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2 5/9] mm/compaction: allow to scan nonmovable pageblock
 when depleted state

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.

> 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.

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