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Subject: Re: [PATCH v2 2/2] mm/pageblock: remove false sharing in
 pageblock_flags
To:     Alex Shi <alex.shi@linux.alibaba.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
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From:   Anshuman Khandual <anshuman.khandual@arm.com>
Message-ID: <715f1588-9cd5-b845-51a5-ca58549c4d28@arm.com>
Date:   Wed, 19 Aug 2020 13:27:04 +0530
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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 ?