linux-kernel - Re: [PATCH v2 0/9] workingset protection/detection on the anonymous LRU list

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Message-ID: <20200228102145.GA675897@ziqianlu-desktop.localdomain>
Date:   Fri, 28 Feb 2020 18:21:45 +0800
From:   Aaron Lu <aaron.lwe@...il.com>
To:     Joonsoo Kim <js1304@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>, kernel-team@....com,
        Huang Ying <ying.huang@...el.com>
Subject: Re: [PATCH v2 0/9] workingset protection/detection on the anonymous
 LRU list

On Fri, Feb 28, 2020 at 06:56:11PM +0900, Joonsoo Kim wrote:
> On Fri, Feb 28, 2020 at 05:17:00PM +0800, Aaron Lu wrote:
> > I think LKP robot has captured these two metrics but the report didn't
> > show them, which means the number is about the same with or without
> > patch #1.
> 
> robot showed these two metrics. See below.
> 
>   50190319 ± 31%     -35.7%   32291856 ± 14%  proc-vmstat.pswpin
>   56429784 ± 21%     -42.6%   32386842 ± 14%  proc-vmstat.pswpout
> 
> pswpin/out are improved.

Oh yes, I checked the vmstat part, while I should check proc-vmstat
part...Sorry for missing this.

> 
> > > with patch #1. With large inactive list, we can easily find the
> > > frequently referenced page and it would result in less swap in/out.
> > 
> > But with small inactive list, the pages that would be on inactive list
> > will stay on active list? I think the larger inactive list is mainly
> > used to give the anon page a chance to be promoted to active list now
> > that anon pages land on inactive list first, but on reclaim, I don't see
> > how a larger inactive list can cause fewer swap outs.
> 
> Point is that larger inactive LRU helps to find hot pages and these
> hot pages leads to more cache hits.
> 
> When a cache hit happens, no swap outs happens. But, if a cache miss
> happens, a new page is added to the LRU and then it causes the reclaim
> and swap out.

OK, I think I start to get your point. Your explanation makes sense.

> > Forgive me for my curiosity and feel free to ignore my question as I
> > don't want to waste your time on this. Your patchset looks a worthwhile
> > thing to do, it's just the robot's report on patch1 seems er...
> 
> I appreciate your attention. Feel free to ask. :)

Thanks a lot for your patience and nice explanation :-)