linux-kernel - Re: [PATCH] mm: vmscan: scan anonymous pages on file refaults

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Message-ID: <20190704094716.GA245276@google.com>
Date:   Thu, 4 Jul 2019 17:47:16 +0800
From:   Kuo-Hsin Yang <vovoy@...omium.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>,
        Sonny Rao <sonnyrao@...omium.org>,
        Kuo-Hsin Yang <vovoy@...omium.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm: vmscan: scan anonymous pages on file refaults

On Wed, Jul 03, 2019 at 04:30:57PM +0200, Michal Hocko wrote:
> 
> How does the reclaim behave with workloads with file backed data set
> not fitting into the memory? Aren't we going to to swap a lot -
> something that the heuristic is protecting from?
> 

In common case, most of the pages in a large file backed data set are
non-executable. When there are a lot of non-executable file pages,
usually more file pages are scanned because of the recent_scanned /
recent_rotated ratio.

I modified the test program to set the accessed sizes of the executable
and non-executable file pages respectively. The test program runs on 2GB
RAM VM with kernel 5.2.0-rc7 and this patch, allocates 2000 MB anonymous
memory, then accesses 100 MB executable file pages and 2100 MB
non-executable file pages for 10 times. The test also prints the file
and anonymous page sizes in kB from /proc/meminfo. There are not too
many swaps in this test case. I got similar test result without this
patch.

$ ./thrash 2000 100 2100 10
Allocate 2000 MB anonymous pages
Active(anon): 1850964, Inactive(anon): 133140, Active(file): 1528, Inactive(file): 1352
Access 100 MB executable file pages
Access 2100 MB regular file pages
File access time, round 0: 26.833665 (sec)
Active(anon): 1476084, Inactive(anon): 492060, Active(file): 2236, Inactive(file): 2224
File access time, round 1: 26.362102 (sec)
Active(anon): 1471364, Inactive(anon): 490464, Active(file): 8508, Inactive(file): 8172
File access time, round 2: 26.828894 (sec)
Active(anon): 1469184, Inactive(anon): 489688, Active(file): 10012, Inactive(file): 9840
File access time, round 3: 27.105603 (sec)
Active(anon): 1468128, Inactive(anon): 489408, Active(file): 11000, Inactive(file): 10388
File access time, round 4: 26.936500 (sec)
Active(anon): 1466380, Inactive(anon): 488788, Active(file): 12872, Inactive(file): 12504
File access time, round 5: 26.294687 (sec)
Active(anon): 1466384, Inactive(anon): 488780, Active(file): 13332, Inactive(file): 12396
File access time, round 6: 27.382404 (sec)
Active(anon): 1466344, Inactive(anon): 488772, Active(file): 13100, Inactive(file): 12276
File access time, round 7: 26.607976 (sec)
Active(anon): 1466392, Inactive(anon): 488764, Active(file): 12892, Inactive(file): 11928
File access time, round 8: 26.477663 (sec)
Active(anon): 1466344, Inactive(anon): 488760, Active(file): 12920, Inactive(file): 12092
File access time, round 9: 26.552859 (sec)
Active(anon): 1465820, Inactive(anon): 488748, Active(file): 13300, Inactive(file): 12372