Re: [PATCH v21 00/19] per memcg lru lock

[Alex Shi]

Hi Andrew,

With all patches are acked-by Hugh and Johannes, and full testing from LKP,
is this patchset ready for more testing on linux-next? or anything still need
be improved?

Thanks
Alex


在 2020/11/5 下午4:55, Alex Shi 写道:
> This version rebase on next/master 20201104, with much of Johannes's
> Acks and some changes according to Johannes comments. And add a new patch
> v21-0006-mm-rmap-stop-store-reordering-issue-on-page-mapp.patch to support
> v21-0007.
> 
> This patchset followed 2 memcg VM_WARN_ON_ONCE_PAGE patches which were
> added to -mm tree yesterday.
>  
> Many thanks for line by line review by Hugh Dickins, Alexander Duyck and
> Johannes Weiner.
> 
> So now this patchset includes 3 parts:
> 1, some code cleanup and minimum optimization as a preparation. 
> 2, use TestCleanPageLRU as page isolation's precondition.
> 3, replace per node lru_lock with per memcg per node lru_lock.
> 
> Current lru_lock is one for each of node, pgdat->lru_lock, that guard for
> lru lists, but now we had moved the lru lists into memcg for long time. Still
> using per node lru_lock is clearly unscalable, pages on each of memcgs have
> to compete each others for a whole lru_lock. This patchset try to use per
> lruvec/memcg lru_lock to repleace per node lru lock to guard lru lists, make
> it scalable for memcgs and get performance gain.
> 
> Currently lru_lock still guards both lru list and page's lru bit, that's ok.
> but if we want to use specific lruvec lock on the page, we need to pin down
> the page's lruvec/memcg during locking. Just taking lruvec lock first may be
> undermined by the page's memcg charge/migration. To fix this problem, we could
> take out the page's lru bit clear and use it as pin down action to block the
> memcg changes. That's the reason for new atomic func TestClearPageLRU.
> So now isolating a page need both actions: TestClearPageLRU and hold the
> lru_lock.
> 
> The typical usage of this is isolate_migratepages_block() in compaction.c
> we have to take lru bit before lru lock, that serialized the page isolation
> in memcg page charge/migration which will change page's lruvec and new 
> lru_lock in it.
> 
> The above solution suggested by Johannes Weiner, and based on his new memcg 
> charge path, then have this patchset. (Hugh Dickins tested and contributed much
> code from compaction fix to general code polish, thanks a lot!).
> 
> Daniel Jordan's testing show 62% improvement on modified readtwice case
> on his 2P * 10 core * 2 HT broadwell box on v18, which has no much different
> with this v20.
> https://lore.kernel.org/lkml/20200915165807.kpp7uhiw7l3loofu@xxxxxxxxxxxxxxxxxxxxxxxxxx/
> 
> Thanks Hugh Dickins and Konstantin Khlebnikov, they both brought this
> idea 8 years ago, and others who give comments as well: Daniel Jordan, 
> Mel Gorman, Shakeel Butt, Matthew Wilcox, Alexander Duyck etc.
> 
> Thanks for Testing support from Intel 0day and Rong Chen, Fengguang Wu,
> and Yun Wang. Hugh Dickins also shared his kbuild-swap case. Thanks!