From: Mel Gorman <mgorman@techsingularity.net>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
David Hildenbrand <david@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
Vlastimil Babka <vbabka@suse.cz>,
Alexander Duyck <alexander.duyck@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 1/4] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags
Date: Thu, 3 Sep 2020 08:24:47 +0100 [thread overview]
Message-ID: <20200903072447.GB3179@techsingularity.net> (raw)
In-Reply-To: <1599116482-7410-1-git-send-email-alex.shi@linux.alibaba.com>
On Thu, Sep 03, 2020 at 03:01:20PM +0800, Alex Shi wrote:
> pageblock_flags is used as long, since every pageblock_flags is just 4
> bits, 'long' size will include 8(32bit machine) or 16 pageblocks' flags,
> that flag setting has to sync in cmpxchg with 7 or 15 other pageblock
> flags. It would cause long waiting for sync.
>
> If we could change the pageblock_flags variable as char, we could use
> char size cmpxchg, which just sync up with 2 pageblock flags. it could
> relief the false sharing in cmpxchg.
>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Page block types were not known to change at high frequency that would
cause a measurable performance drop. If anything, the performance hit
from pageblocks is the lookup paths which is a lot more frequent.
What was the workload you were running that altered pageblocks at a high
enough frequency for collisions to occur when updating adjacent
pageblocks?
--
Mel Gorman
SUSE Labs
next prev parent reply other threads:[~2020-09-03 7:24 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 7:01 [PATCH v4 1/4] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Alex Shi
2020-09-03 7:01 ` [PATCH v4 2/4] mm/pageblock: remove false sharing in pageblock_flags Alex Shi
2020-09-03 7:01 ` [PATCH v4 3/4] mm/pageblock: work around multiple arch's cmpxchg support issue Alex Shi
2020-09-03 7:01 ` Alex Shi
2020-09-03 7:01 ` Alex Shi
2020-09-03 7:29 ` Max Filippov
2020-09-03 7:29 ` Max Filippov
2020-09-03 7:29 ` Max Filippov
2020-09-03 8:50 ` Alex Shi
2020-09-03 8:50 ` Alex Shi
2020-09-03 8:50 ` Alex Shi
2020-09-10 5:51 ` Christoph Hellwig
2020-09-10 5:51 ` Christoph Hellwig
2020-09-10 5:51 ` Christoph Hellwig
2020-09-03 7:24 ` Mel Gorman [this message]
2020-09-03 8:32 ` [PATCH v4 1/4] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Alex Shi
2020-09-03 8:40 ` Alex Shi
2020-09-03 9:00 ` Vlastimil Babka
2020-09-03 9:31 ` Mel Gorman
2020-09-03 8:19 ` David Hildenbrand
2020-09-03 9:14 ` Alex Shi
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