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From: Alex Shi <alex.shi@linux.alibaba.com>
To: Anshuman Khandual <anshuman.khandual@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	David Hildenbrand <david@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Hugh Dickins <hughd@google.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 2/2] mm/pageblock: remove false sharing in pageblock_flags
Date: Wed, 19 Aug 2020 16:09:51 +0800	[thread overview]
Message-ID: <a7376a9c-82e8-7dc1-b656-9c0516738801@linux.alibaba.com> (raw)
In-Reply-To: <715f1588-9cd5-b845-51a5-ca58549c4d28@arm.com>



在 2020/8/19 下午3:57, Anshuman Khandual 写道:
> 
> 
> On 08/19/2020 11:17 AM, Alex Shi wrote:
>> Current pageblock_flags is only 4 bits, so it has to share a char size
>> in cmpxchg when get set, the false sharing cause perf drop.
>>
>> If we incrase the bits up to 8, false sharing would gone in cmpxchg. and
>> the only cost is half char per pageblock, which is half char per 128MB
>> on x86, 4 chars in 1 GB.
> 
> Agreed that increase in memory utilization is negligible here but does
> this really improve performance ?
> 

It's no doubt in theory. and it would had a bad impact according to 
commit e380bebe4771548  mm, compaction: keep migration source private to a single 

but I do have some problem in running thpscale/mmtest. I'd like to see if anyone
could give a try.

BTW, I naturally hate the false sharing even it's in theory. Anyone who doesn't? :)

Thanks
Alex 

  reply	other threads:[~2020-08-19  8:11 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-19  5:47 [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Alex Shi
2020-08-19  5:47 ` [PATCH v2 2/2] mm/pageblock: remove false sharing in pageblock_flags Alex Shi
2020-08-19  7:57   ` Anshuman Khandual
2020-08-19  8:09     ` Alex Shi [this message]
2020-08-19  8:13       ` David Hildenbrand
2020-08-19  8:36         ` Alex Shi
2020-08-19 16:50       ` Alexander Duyck
2020-08-30 10:00         ` Alex Shi
2020-08-30 20:32           ` Alexander Duyck
2020-09-03  5:35             ` Alex Shi
2020-09-01 17:04       ` Vlastimil Babka
2020-08-19  7:55 ` [PATCH v2 1/2] mm/pageblock: mitigation cmpxchg false sharing in pageblock flags Anshuman Khandual
2020-08-19  8:04   ` David Hildenbrand
2020-08-30 10:08     ` Alex Shi
2020-08-30 10:14   ` Alex Shi
2020-08-30 10:18     ` Matthew Wilcox
2020-08-31  8:40       ` Alex Shi

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