From: Shaohua Li <shli@kernel.org>
To: Mel Gorman <mgorman@suse.de>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org, aarcange@redhat.com
Subject: Re: [patch 1/2]compaction: check migrated page number
Date: Thu, 6 Sep 2012 20:55:26 +0800 [thread overview]
Message-ID: <20120906125526.GA1025@kernel.org> (raw)
In-Reply-To: <20120906121725.GQ11266@suse.de>
On Thu, Sep 06, 2012 at 01:17:25PM +0100, Mel Gorman wrote:
> On Thu, Sep 06, 2012 at 06:44:04PM +0800, Shaohua Li wrote:
> >
> > isolate_migratepages_range() might isolate none pages, for example, when
> > zone->lru_lock is contended and compaction is async. In this case, we should
> > abort compaction, otherwise, compact_zone will run a useless loop and make
> > zone->lru_lock is even contended.
> >
>
> It might also isolate no pages because the range was 100% allocated and
> there were no free pages to isolate. This is perfectly normal and I suspect
> this patch effectively disables compaction. What problem did you observe
> that this patch is aimed at?
I'm running a random swapin/out workload. When memory is fragmented enough, I
saw 100% cpu usage. perf shows zone->lru_lock is heavily contended in
isolate_migratepages_range. I'm using slub(I didn't see the problem with slab),
the allocation is for radix_tree_node slab, which needs 4 pages. Even If I just
apply the second patch, the system is still in 100% cpu usage. The
spin_is_contended check can't cure the problem completely. Trace shows
compact_zone will run a useless loop and each loop contend the lru_lock. With
this patch, the cpu usage becomes normal (about 20% utilization).
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next prev parent reply other threads:[~2012-09-06 12:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-06 10:44 [patch 1/2]compaction: check migrated page number Shaohua Li
2012-09-06 12:17 ` Mel Gorman
2012-09-06 12:55 ` Shaohua Li [this message]
2012-09-06 13:25 ` Mel Gorman
2012-09-07 4:12 ` Shaohua Li
2012-09-07 15:52 ` Andrea Arcangeli
2012-09-10 1:05 ` Shaohua Li
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