linux-kernel - Re: [PATCH v18 20/32] mm/lru: replace pgdat lru

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Date:   Tue, 22 Sep 2020 16:58:47 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     akpm@...ux-foundation.org, mgorman@...hsingularity.net,
        tj@...nel.org, khlebnikov@...dex-team.ru,
        daniel.m.jordan@...cle.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, kirill@...temov.name,
        alexander.duyck@...il.com, rong.a.chen@...el.com, mhocko@...e.com,
        vdavydov.dev@...il.com, shy828301@...il.com,
        Michal Hocko <mhocko@...nel.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>
Subject: Re: [PATCH v18 20/32] mm/lru: replace pgdat lru_lock with lruvec lock



在 2020/9/22 下午1:27, Hugh Dickins 写道:
> On Mon, 24 Aug 2020, Alex Shi wrote:
> 
>> This patch 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.
>>
>> After move memcg charge before lru inserting, page isolation could
>> serialize page's memcg, then per memcg lruvec lock is stable and could
>> replace per node lru lock.
>>
>> In func isolate_migratepages_block, compact_unlock_should_abort is
>> opend, and lock_page_lruvec logical is embedded for tight process.
> 
> Hard to understand: perhaps:
> 
> In func isolate_migratepages_block, compact_unlock_should_abort and
> lock_page_lruvec_irqsave are open coded to work with compact_control.

will update with your suggestion. Thanks!

> 
>> Also add a debug func in locking which may give some clues if there are
>> sth out of hands.
>>
>> According to Daniel Jordan's suggestion, I 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
> 
> s/modeified/modified/
> lruv19 has an lkml.org link there, please substitut
> https://lore.kernel.org/lkml/01ed6e45-3853-dcba-61cb-b429a49a7572@linux.alibaba.com/
> 

Thanks!

>>
>> With this and later patches, the readtwice performance increases
>> about 80% within concurrent containers.
>>
>> On a large machine with memcg enabled but not used, the page's lruvec
>> seeking pass a few pointers, that may lead to lru_lock holding time
>> increase and a bit regression.
>>
>> Hugh Dickins helped on patch polish, thanks!
>>
>> Reported-by: kernel test robot <lkp@...el.com>
> 
> Eh? It may have reported some locking bugs somewhere, but this
> is the main patch of your per-memcg lru_lock: I don't think the
> kernel test robot inspired your whole design, did it?  Delete that.
> 
> 
>> Signed-off-by: Alex Shi <alex.shi@...ux.alibaba.com>
> 
> I can't quite Ack this one yet, because there are several functions
> (mainly __munlock_pagevec and check_move_unevictable_pages) which are
> not right in this v18 version, and a bit tricky to correct: I already
> suggested what to do in other mail, but this patch comes before
> relock_page_lruvec, so must look different from the final result;
> I need to look at a later version, perhaps already there in your
> github tree, before I can Ack: but it's not far off.
> Comments below.

All suggestions are taken! Many thanks for so detailed review!
A new branch with all comments is updated as 
    https://github.com/alexshi/linux.git lruv19.5

A quick summary for the branch,
Add a new patch for move_pages_to_lru:
	mm/vmscan: remove lruvec reget in move_pages_to_lru
Add another patch for split part from 'Introduce TestClearPageLRU':
 	mm/swap.c: reorder __ClearPageLRU and lruvec

the mlock changes moved earlier:
	mm/mlock: remove __munlock_isolate_lru_page
	mm/mlock: remove __munlock_isolate_lru_page

I am wondering if it's good to send out v19 here or maybe better to wait
for your confirm if all suggestion/comments are settled?

Thanks
Alex