From: Mel Gorman <mel@csn.ul.ie>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
Andrew Morton <akpm@linux-foundation.org>,
Rik van Riel <riel@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 7/8] mm: compaction: Use the LRU to get a hint on where compaction should start
Date: Thu, 18 Nov 2010 09:28:12 +0000 [thread overview]
Message-ID: <20101118092812.GF8135@csn.ul.ie> (raw)
In-Reply-To: <20101118181048.7bdfbb38.kamezawa.hiroyu@jp.fujitsu.com>
On Thu, Nov 18, 2010 at 06:10:48PM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 17 Nov 2010 16:22:48 +0000
> Mel Gorman <mel@csn.ul.ie> wrote:
>
> > The end of the LRU stores the oldest known page. Compaction on the other
> > hand always starts scanning from the start of the zone. This patch uses
> > the LRU to hint to compaction where it should start scanning from. This
> > means that compaction will at least start with some old pages reducing
> > the impact on running processes and reducing the amount of scanning. The
> > check it makes is racy as the LRU lock is not taken but it should be
> > harmless as we are not manipulating the lists without the lock.
> >
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
>
> Hmm, does this patch make a noticable difference ?
To scanning rates - yes.
> Isn't it better to start scan from the biggest free chunk in a zone ?
>
Not necessarily. The biggest free chunk does not necessarily contain old
pages so one could stall a process by migrating a very active page. The same
applies for selecting the pageblock with the oldest LRU page of course but
it is less likely.
I prototyped a a patch that constantly used the buddy lists to select the
next pageblock to migrate from. The problem was that it was possible for it
to infinite loop because it could migrate from the same block more than once
in a migration cycle. To resolve that, I'd have to keep track of visited
pageblocks but I didn't want to require additional memory unless it was
absolutly necessary. I think the concept can be perfected and its impact
would be a reduction of scanning rates but it's not something that is
anywhere near merging yet.
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
next prev parent reply other threads:[~2010-11-18 9:28 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-17 16:22 [PATCH 0/8] Use memory compaction instead of lumpy reclaim during high-order allocations Mel Gorman
2010-11-17 16:22 ` [PATCH 1/8] mm: compaction: Add trace events for memory compaction activity Mel Gorman
2010-11-17 16:22 ` [PATCH 2/8] mm: vmscan: Convert lumpy_mode into a bitmask Mel Gorman
2010-11-17 16:22 ` [PATCH 3/8] mm: vmscan: Reclaim order-0 and use compaction instead of lumpy reclaim Mel Gorman
2010-11-18 18:09 ` Andrea Arcangeli
2010-11-18 18:30 ` Mel Gorman
2010-11-17 16:22 ` [PATCH 4/8] mm: migration: Allow migration to operate asynchronously and avoid synchronous compaction in the faster path Mel Gorman
2010-11-18 18:21 ` Andrea Arcangeli
2010-11-18 18:34 ` Mel Gorman
2010-11-18 19:00 ` Andrea Arcangeli
2010-11-17 16:22 ` [PATCH 5/8] mm: migration: Cleanup migrate_pages API by matching types for offlining and sync Mel Gorman
2010-11-17 16:22 ` [PATCH 6/8] mm: compaction: Perform a faster scan in try_to_compact_pages() Mel Gorman
2010-11-18 18:34 ` Andrea Arcangeli
2010-11-18 18:50 ` Mel Gorman
2010-11-18 19:08 ` Andrea Arcangeli
2010-11-19 11:16 ` Mel Gorman
2010-11-17 16:22 ` [PATCH 7/8] mm: compaction: Use the LRU to get a hint on where compaction should start Mel Gorman
2010-11-18 9:10 ` KAMEZAWA Hiroyuki
2010-11-18 9:28 ` Mel Gorman [this message]
2010-11-18 18:46 ` Andrea Arcangeli
2010-11-19 11:08 ` Mel Gorman
2010-11-17 16:22 ` [PATCH 8/8] mm: vmscan: Rename lumpy_mode to reclaim_mode Mel Gorman
2010-11-17 23:46 ` [PATCH 0/8] Use memory compaction instead of lumpy reclaim during high-order allocations Andrew Morton
2010-11-18 2:03 ` Rik van Riel
2010-11-18 8:12 ` Mel Gorman
2010-11-18 8:26 ` KAMEZAWA Hiroyuki
2010-11-18 8:38 ` Johannes Weiner
2010-11-18 9:20 ` Mel Gorman
2010-11-18 19:49 ` Andrew Morton
2010-11-19 10:48 ` Mel Gorman
2010-11-19 12:43 ` Theodore Tso
2010-11-19 14:05 ` Mel Gorman
2010-11-19 15:45 ` Ted Ts'o
2010-11-18 8:44 ` Mel Gorman
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