From: David Hildenbrand <david@redhat.com>
To: Alex Shi <alex.shi@linux.alibaba.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Matthew Wilcox <willy@infradead.org>
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 10:13:20 +0200 [thread overview]
Message-ID: <0dc33af2-4d2d-9531-03fa-d26654ab79fb@redhat.com> (raw)
In-Reply-To: <a7376a9c-82e8-7dc1-b656-9c0516738801@linux.alibaba.com>
On 19.08.20 10:09, Alex Shi wrote:
>
>
> 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? :)
I hate wasting memory, even if it's just a little bit, anyone who
doesn't? ;)
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-08-19 8:13 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
2020-08-19 8:13 ` David Hildenbrand [this message]
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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