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

Alex Shi
2020-11-26T03:13:00Z

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.