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

[Kuo-Hsin Yang]

On Thu, Jul 04, 2019 at 01:04:25PM +0200, Michal Hocko wrote:
> On Thu 04-07-19 17:47:16, Kuo-Hsin Yang wrote:
> > 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.
> 
> Could you record swap out stats please? Also what happens if you have
> multiple readers?

Checked the swap out stats during the test [1], 19006 pages swapped out
with this patch, 3418 pages swapped out without this patch. There are
more swap out, but I think it's within reasonable range when file backed
data set doesn't fit into the memory.

$ ./thrash 2000 100 2100 5 1 # ANON_MB FILE_EXEC FILE_NOEXEC ROUNDS PROCESSES
Allocate 2000 MB anonymous pages
active_anon: 1613644, inactive_anon: 348656, active_file: 892, inactive_file: 1384 (kB)
pswpout: 7972443, pgpgin: 478615246
Access 100 MB executable file pages
Access 2100 MB regular file pages
File access time, round 0: 12.165, (sec)
active_anon: 1433788, inactive_anon: 478116, active_file: 17896, inactive_file: 24328 (kB)
File access time, round 1: 11.493, (sec)
active_anon: 1430576, inactive_anon: 477144, active_file: 25440, inactive_file: 26172 (kB)
File access time, round 2: 11.455, (sec)
active_anon: 1427436, inactive_anon: 476060, active_file: 21112, inactive_file: 28808 (kB)
File access time, round 3: 11.454, (sec)
active_anon: 1420444, inactive_anon: 473632, active_file: 23216, inactive_file: 35036 (kB)
File access time, round 4: 11.479, (sec)
active_anon: 1413964, inactive_anon: 471460, active_file: 31728, inactive_file: 32224 (kB)
pswpout: 7991449 (+ 19006), pgpgin: 489924366 (+ 11309120)

With 4 processes accessing non-overlapping parts of a large file, 30316
pages swapped out with this patch, 5152 pages swapped out without this
patch. The swapout number is small comparing to pgpgin.

[1]: https://github.com/vovo/testing/blob/master/mem_thrash.c