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Subject: Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     Konstantin Khlebnikov <koct9i@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Hugh Dickins <hughd@google.com>, Yu Zhao <yuzhao@google.com>,
        Michal Hocko <mhocko@suse.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <1605860847-47445-1-git-send-email-alex.shi@linux.alibaba.com>
 <b92a1a50-b7cd-0b33-de2e-52d74c91925c@suse.cz>
From:   Alex Shi <alex.shi@linux.alibaba.com>
Message-ID: <df62191b-e694-1928-2ffc-c4cfb4dea14d@linux.alibaba.com>
Date:   Thu, 26 Nov 2020 11:12:30 +0800
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在 2020/11/25 下午11:38, Vlastimil Babka 写道:
> On 11/20/20 9:27 AM, Alex Shi wrote:
>> The current relock logical will change lru_lock when found a new
>> lruvec, so if 2 memcgs are reading file or alloc page at same time,
>> they could hold the lru_lock alternately, and wait for each other for
>> fairness attribute of ticket spin lock.
>>
>> This patch will sort that all lru_locks and only hold them once in
>> above scenario. That could reduce fairness waiting for lock reget.
>> Than, vm-scalability/case-lru-file-readtwice could get ~5% performance
>> gain on my 2P*20core*HT machine.
> 
> Hm, once you sort the pages like this, it's a shame not to splice them instead of more list_del() + list_add() iterations. update_lru_size() could be also called once?

Yes, looks it's a good idea to use splice instead of list_del/add, but pages
may on different lru list in a same lruvec, and also may come from different
zones. That could involve 5 cycles for different lists, and more for zones...

I give up the try.