From: Rik van Riel <riel@redhat.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Richard Davies <richard@arachsys.com>, KVM <kvm@vger.kernel.org>,
QEMU-devel <qemu-devel@nongnu.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Avi Kivity <avi@redhat.com>,
Shaohua Li <shli@kernel.org>
Subject: Re: [Qemu-devel] [PATCH 6/6] mm: compaction: Restart compaction from near where it left off
Date: Thu, 20 Sep 2012 14:57:10 -0400 [thread overview]
Message-ID: <505B6706.1000104@redhat.com> (raw)
In-Reply-To: <1348149875-29678-7-git-send-email-mgorman@suse.de>
On 09/20/2012 10:04 AM, Mel Gorman wrote:
> This is almost entirely based on Rik's previous patches and discussions
> with him about how this might be implemented.
>
> Order > 0 compaction stops when enough free pages of the correct page
> order have been coalesced. When doing subsequent higher order allocations,
> it is possible for compaction to be invoked many times.
>
> However, the compaction code always starts out looking for things to compact
> at the start of the zone, and for free pages to compact things to at the
> end of the zone.
>
> This can cause quadratic behaviour, with isolate_freepages starting at
> the end of the zone each time, even though previous invocations of the
> compaction code already filled up all free memory on that end of the zone.
> This can cause isolate_freepages to take enormous amounts of CPU with
> certain workloads on larger memory systems.
>
> This patch caches where the migration and free scanner should start from on
> subsequent compaction invocations using the pageblock-skip information. When
> compaction starts it begins from the cached restart points and will
> update the cached restart points until a page is isolated or a pageblock
> is skipped that would have been scanned by synchronous compaction.
>
> Signed-off-by: Mel Gorman <mgorman@suse.de>
Together with patch 5/6, this has the effect of
skipping compaction in a zone if the free and
isolate markers have met, and it has been less
than 5 seconds since the "skip" information was
reset.
Compaction on zones where we cycle through more
slowly can continue, even when this particular
zone is experiencing problems, so I guess this
is desired behaviour...
Acked-by: Rik van Riel <riel@redhat.com>
next prev parent reply other threads:[~2012-09-20 18:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-20 14:04 [Qemu-devel] [PATCH 0/6] Reduce compaction scanning and lock contention Mel Gorman
2012-09-20 14:04 ` [Qemu-devel] [PATCH 1/6] mm: compaction: Abort compaction loop if lock is contended or run too long Mel Gorman
2012-09-20 18:53 ` Rik van Riel
2012-09-20 14:04 ` [Qemu-devel] [PATCH 2/6] mm: compaction: Acquire the zone->lru_lock as late as possible Mel Gorman
2012-09-20 18:54 ` Rik van Riel
2012-09-20 14:04 ` [Qemu-devel] [PATCH 3/6] mm: compaction: Acquire the zone->lock " Mel Gorman
2012-09-20 18:54 ` Rik van Riel
2012-09-20 14:04 ` [Qemu-devel] [PATCH 4/6] Revert "mm: have order > 0 compaction start off where it left" Mel Gorman
2012-09-20 18:54 ` Rik van Riel
2012-09-20 14:04 ` [Qemu-devel] [PATCH 5/6] mm: compaction: Cache if a pageblock was scanned and no pages were isolated Mel Gorman
2012-09-20 18:55 ` Rik van Riel
2012-09-20 14:04 ` [Qemu-devel] [PATCH 6/6] mm: compaction: Restart compaction from near where it left off Mel Gorman
2012-09-20 18:57 ` Rik van Riel [this message]
2012-09-21 9:13 ` [Qemu-devel] [PATCH 0/6] Reduce compaction scanning and lock contention Richard Davies
2012-09-21 9:15 ` Richard Davies
2012-09-21 9:17 ` Richard Davies
2012-09-21 9:55 ` Mel Gorman
2012-09-21 9:18 ` Richard Davies
2012-09-21 9:35 ` Mel Gorman
2012-09-21 9:49 ` Richard Davies
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