From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, Johannes Weiner <hannes@cmpxchg.org>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
David Rientjes <rientjes@google.com>,
linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH v2 03/10] mm, page_alloc: split smallest stolen page in fallback
Date: Mon, 13 Feb 2017 10:51:18 +0000 [thread overview]
Message-ID: <20170213105118.f3y5y2xaf2kdnxv7@techsingularity.net> (raw)
In-Reply-To: <20170210172343.30283-4-vbabka@suse.cz>
On Fri, Feb 10, 2017 at 06:23:36PM +0100, Vlastimil Babka wrote:
> The __rmqueue_fallback() function is called when there's no free page of
> requested migratetype, and we need to steal from a different one. There are
> various heuristics to make this event infrequent and reduce permanent
> fragmentation. The main one is to try stealing from a pageblock that has the
> most free pages, and possibly steal them all at once and convert the whole
> pageblock. Precise searching for such pageblock would be expensive, so instead
> the heuristics walks the free lists from MAX_ORDER down to requested order and
> assumes that the block with highest-order free page is likely to also have the
> most free pages in total.
>
> Chances are that together with the highest-order page, we steal also pages of
> lower orders from the same block. But then we still split the highest order
> page. This is wasteful and can contribute to fragmentation instead of avoiding
> it.
>
The original intent was that if an allocation request was stealing a
pageblock that taking the largest one would reduce the likelihood of a
steal in the near future by the same type.
> This patch thus changes __rmqueue_fallback() to just steal the page(s) and put
> them on the freelist of the requested migratetype, and only report whether it
> was successful. Then we pick (and eventually split) the smallest page with
> __rmqueue_smallest(). This all happens under zone lock, so nobody can steal it
> from us in the process. This should reduce fragmentation due to fallbacks. At
> worst we are only stealing a single highest-order page and waste some cycles by
> moving it between lists and then removing it, but fallback is not exactly hot
> path so that should not be a concern. As a side benefit the patch removes some
> duplicate code by reusing __rmqueue_smallest().
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
But conceptually this is better so
Acked-by: Mel Gorman <mgorman@techsingularity.net>
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2017-02-13 10:51 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-10 17:23 [PATCH v2 00/10] try to reduce fragmenting fallbacks Vlastimil Babka
2017-02-10 17:23 ` [PATCH v2 01/10] mm, compaction: reorder fields in struct compact_control Vlastimil Babka
2017-02-13 10:49 ` Mel Gorman
2017-02-14 16:33 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 02/10] mm, compaction: remove redundant watermark check in compact_finished() Vlastimil Babka
2017-02-13 10:49 ` Mel Gorman
2017-02-14 16:34 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 03/10] mm, page_alloc: split smallest stolen page in fallback Vlastimil Babka
2017-02-13 10:51 ` Mel Gorman [this message]
2017-02-13 10:54 ` Vlastimil Babka
2017-02-14 16:59 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 04/10] mm, page_alloc: count movable pages when stealing from pageblock Vlastimil Babka
2017-02-13 10:53 ` Mel Gorman
2017-02-14 10:07 ` Xishi Qiu
2017-02-15 10:47 ` Vlastimil Babka
2017-02-15 11:56 ` Xishi Qiu
2017-02-17 16:21 ` Vlastimil Babka
2017-02-14 18:10 ` Johannes Weiner
2017-02-17 16:09 ` Vlastimil Babka
2017-02-10 17:23 ` [PATCH v2 05/10] mm, compaction: change migrate_async_suitable() to suitable_migration_source() Vlastimil Babka
2017-02-13 10:53 ` Mel Gorman
2017-02-14 18:12 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 06/10] mm, compaction: add migratetype to compact_control Vlastimil Babka
2017-02-13 10:53 ` Mel Gorman
2017-02-14 18:15 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 07/10] mm, compaction: restrict async compaction to pageblocks of same migratetype Vlastimil Babka
2017-02-13 10:56 ` Mel Gorman
2017-02-14 20:10 ` Johannes Weiner
2017-02-17 16:32 ` Vlastimil Babka
2017-02-17 17:39 ` Johannes Weiner
2017-02-10 17:23 ` [PATCH v2 08/10] mm, compaction: finish whole pageblock to reduce fragmentation Vlastimil Babka
2017-02-13 10:57 ` Mel Gorman
2017-02-16 11:44 ` Johannes Weiner
2017-02-10 17:23 ` [RFC v2 09/10] mm, page_alloc: disallow migratetype fallback in fastpath Vlastimil Babka
2017-02-10 17:23 ` [RFC v2 10/10] mm, page_alloc: introduce MIGRATE_MIXED migratetype Vlastimil Babka
2017-03-08 2:16 ` Yisheng Xie
2017-03-08 7:07 ` Vlastimil Babka
2017-03-13 2:16 ` Yisheng Xie
2017-02-13 11:07 ` [PATCH v2 00/10] try to reduce fragmenting fallbacks Mel Gorman
2017-02-15 14:29 ` Vlastimil Babka
2017-02-15 16:11 ` Vlastimil Babka
2017-02-15 20:11 ` Vlastimil Babka
2017-02-16 15:12 ` Vlastimil Babka
2017-02-17 15:24 ` Vlastimil Babka
2017-02-20 12:30 ` Vlastimil Babka
2017-02-23 16:01 ` Mel Gorman
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