linux-kernel - Re: [PATCH v9 07/20] mm/lru: introduce TestClearPageLRU

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Date:   Tue, 3 Mar 2020 12:11:34 +0800
From:   Alex Shi <alex.shi@...ux.alibaba.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     cgroups@...r.kernel.org, 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,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v9 07/20] mm/lru: introduce TestClearPageLRU



在 2020/3/3 上午6:11, Andrew Morton 写道:
>> -		if (PageLRU(page)) {
>> +		if (TestClearPageLRU(page)) {
>>  			lruvec = mem_cgroup_page_lruvec(page, pgdat);
>> -			ClearPageLRU(page);
>>  			del_page_from_lru_list(page, lruvec, page_lru(page));
>>  		} else
> 
> The code will now get exclusive access of the page->flags cacheline and
> will dirty that cacheline, even for !PageLRU() pages.  What is the
> performance impact of this?
> 

Hi Andrew,

Thanks a lot for comments!

I was tested the whole patchset with fengguang's case-lru-file-readtwice
https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git/
which is most sensitive case on PageLRU I found. There are no clear performance
drop.

On this single patch, I just test the same case again, there is still no perf
drop. some data is here on my 96 threads machine:

		no lock_dep	w lock_dep and few other debug option
w this patch, 	50.96MB/s		32.93MB/s
w/o this patch, 50.50MB/s		33.53MB/s


And also no any warning from Intel 0day yet.

Thanks a lot!
Alex