Re: [PATCH next] mm/swap.c: reduce lock contention in lru_cache_add

Alex Shi
2020-11-23T04:48:44Z

在 2020/11/21 上午7:19, Andrew Morton 写道:
> On Fri, 20 Nov 2020 16:27:27 +0800 Alex Shi <alex.shi@linux.alibaba.com> 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.
>
> But what happens when all or most of the pages belong to the same
> lruvec? This sounds like the common case - won't it suffer?
>
Hi Andrew,

My testing show no regression on this situation, like original centos7,
The most spending time is on lru_lock for lru sensitive case.

Thanks
Alex