linux-kernel - Re: [PATCH v13 00/18] per memcg lru lock

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Date:   Sat, 20 Jun 2020 16:08:07 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     mgorman@...hsingularity.net, tj@...nel.org, hughd@...gle.com,
        khlebnikov@...dex-team.ru, daniel.m.jordan@...cle.com,
        yang.shi@...ux.alibaba.com, willy@...radead.org,
        hannes@...xchg.org, lkp@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        shakeelb@...gle.com, iamjoonsoo.kim@....com,
        richard.weiyang@...il.com
Subject: Re: [PATCH v13 00/18] per memcg lru lock

On Fri, 19 Jun 2020 16:33:38 +0800 Alex Shi <alex.shi@...ux.alibaba.com> wrote:

> This is a new version which bases on linux-next, merged much suggestion
> from Hugh Dickins, from compaction fix to less TestClearPageLRU and
> comments reverse etc. Thank a lot, Hugh!
> 
> Johannes Weiner has suggested:
> "So here is a crazy idea that may be worth exploring:
> 
> Right now, pgdat->lru_lock protects both PageLRU *and* the lruvec's
> linked list.
> 
> Can we make PageLRU atomic and use it to stabilize the lru_lock
> instead, and then use the lru_lock only serialize list operations?

I don't understand this sentence.  How can a per-page flag stabilize a
per-pgdat spinlock?  Perhaps some additional description will help.

> ..."
> 
> With new memcg charge path and this solution, we could isolate
> LRU pages to exclusive visit them in compaction, page migration, reclaim,
> memcg move_accunt, huge page split etc scenarios while keeping pages' 
> memcg stable. Then possible to change per node lru locking to per memcg
> lru locking. As to pagevec_lru_move_fn funcs, it would be safe to let
> pages remain on lru list, lru lock could guard them for list integrity.
> 
> The 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
> 
> The 3rd part moves per node lru_lock into lruvec, thus bring a lru_lock for
> each of memcg per node. So on a large machine, each of memcg don't
> have to suffer from per node pgdat->lru_lock competition. They could go
> fast with their self lru_lock
> 
> Following Daniel Jordan's suggestion, I have run 208 'dd' with on 104
> containers on a 2s * 26cores * HT box with a modefied case:
> https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git/tree/case-lru-file-readtwice
> 
> With this patchset, the readtwice performance increased about 80%
> in concurrent containers.
> 
> 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 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!
> 
> ...
>
>  24 files changed, 500 insertions(+), 357 deletions(-)

It's a large patchset and afaict the whole point is performance gain. 
80% in one specialized test sounds nice, but is there a plan for more
extensive quantification?

There isn't much sign of completed review activity here, so I'll go
into hiding for a while.