From: Mel Gorman <mgorman@suse.de>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 5/5] mm: compaction: reset scanner positions immediately when they meet
Date: Tue, 26 Nov 2013 11:03:30 +0000 [thread overview]
Message-ID: <20131126110330.GJ5285@suse.de> (raw)
In-Reply-To: <1385389570-11393-6-git-send-email-vbabka@suse.cz>
On Mon, Nov 25, 2013 at 03:26:10PM +0100, Vlastimil Babka wrote:
> Compaction used to start its migrate and free page scaners at the zone's lowest
> and highest pfn, respectively. Later, caching was introduced to remember the
> scanners' progress across compaction attempts so that pageblocks are not
> re-scanned uselessly. Additionally, pageblocks where isolation failed are
> marked to be quickly skipped when encountered again in future compactions.
>
> Currently, both the reset of cached pfn's and clearing of the pageblock skip
> information for a zone is done in __reset_isolation_suitable(). This function
> gets called when:
> - compaction is restarting after being deferred
> - compact_blockskip_flush flag is set in compact_finished() when the scanners
> meet (and not again cleared when direct compaction succeeds in allocation)
> and kswapd acts upon this flag before going to sleep
>
> This behavior is suboptimal for several reasons:
> - when direct sync compaction is called after async compaction fails (in the
> allocation slowpath), it will effectively do nothing, unless kswapd
> happens to process the compact_blockskip_flush flag meanwhile. This is racy
> and goes against the purpose of sync compaction to more thoroughly retry
> the compaction of a zone where async compaction has failed.
> The restart-after-deferring path cannot help here as deferring happens only
> after the sync compaction fails. It is also done only for the preferred
> zone, while the compaction might be done for a fallback zone.
> - the mechanism of marking pageblock to be skipped has little value since the
> cached pfn's are reset only together with the pageblock skip flags. This
> effectively limits pageblock skip usage to parallel compactions.
>
> This patch changes compact_finished() so that cached pfn's are reset
> immediately when the scanners meet. Clearing pageblock skip flags is unchanged,
> as well as the other situations where cached pfn's are reset. This allows the
> sync-after-async compaction to retry pageblocks not marked as skipped, such as
> blocks !MIGRATE_MOVABLE blocks that async compactions now skips without
> marking them.
>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rik van Riel <riel@redhat.com>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@suse.de>
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2013-11-26 11:03 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-25 14:26 [RFC PATCH 0/5] Memory compaction efficiency improvements Vlastimil Babka
2013-11-25 14:26 ` [PATCH 1/5] mm: compaction: encapsulate defer reset logic Vlastimil Babka
2013-11-25 22:08 ` Rik van Riel
2013-11-26 10:16 ` Mel Gorman
2013-11-25 14:26 ` [PATCH 2/5] mm: compaction: reset cached scanner pfn's before reading them Vlastimil Babka
2013-11-26 10:23 ` Mel Gorman
2013-11-26 13:16 ` Rik van Riel
2013-11-25 14:26 ` [PATCH 3/5] mm: compaction: detect when scanners meet in isolate_freepages Vlastimil Babka
2013-11-26 10:45 ` Mel Gorman
2013-11-26 16:44 ` Vlastimil Babka
2013-11-25 14:26 ` [PATCH 4/5] mm: compaction: do not mark unmovable pageblocks as skipped in async compaction Vlastimil Babka
2013-11-26 10:58 ` Mel Gorman
2013-11-25 14:26 ` [PATCH 5/5] mm: compaction: reset scanner positions immediately when they meet Vlastimil Babka
2013-11-26 11:03 ` Mel Gorman [this message]
2013-12-04 14:30 ` [PATCH] mm: compaction: Trace compaction begin and end Mel Gorman
2013-12-04 14:51 ` Vlastimil Babka
2013-12-05 9:05 ` Mel Gorman
2013-12-06 9:50 ` Vlastimil Babka
2013-12-05 9:07 ` [PATCH] mm: compaction: Trace compaction begin and end v2 Mel Gorman
2013-12-06 9:50 ` Vlastimil Babka
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