Messages in this thread | | | Date | Mon, 8 Aug 2011 16:18:11 +0400 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH 1/2] vmscan: promote shared file mapped pages |
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Pekka Enberg wrote: > Hi Konstantin, > > On Mon, Aug 8, 2011 at 2:06 PM, Konstantin Khlebnikov > <khlebnikov@openvz.org> wrote: >> Commit v2.6.33-5448-g6457474 (vmscan: detect mapped file pages used only once) >> greatly decreases lifetime of single-used mapped file pages. >> Unfortunately it also decreases life time of all shared mapped file pages. >> Because after commit v2.6.28-6130-gbf3f3bc (mm: don't mark_page_accessed in fault path) >> page-fault handler does not mark page active or even referenced. >> >> Thus page_check_references() activates file page only if it was used twice while >> it stays in inactive list, meanwhile it activates anon pages after first access. >> Inactive list can be small enough, this way reclaimer can accidentally >> throw away any widely used page if it wasn't used twice in short period. >> >> After this patch page_check_references() also activate file mapped page at first >> inactive list scan if this page is already used multiple times via several ptes. >> >> Signed-off-by: Konstantin Khlebnikov<khlebnikov@openvz.org> > > Both patches seem reasonable but the changelogs don't really explain > why you're doing the changes. How did you find out about the problem? > Is there some workload that's affected? How did you test your changes? >
I found this while trying to fix degragation in rhel6 (~2.6.32) from rhel5 (~2.6.18). There a complete mess with >100 web/mail/spam/ftp containers, they share all their files but there a lot of anonymous pages: ~500mb shared file mapped memory and 15-20Gb non-shared anonymous memory. In this situation major-pagefaults are very costly, because all containers share the same page. In my load kernel created a disproportionate pressure on the file memory, compared with the anonymous, they equaled only if I raise swappiness up to 150 =)
These patches actually wasn't helped a lot in my problem, but I saw noticable (10-20 times) reduce in count and average time of major-pagefault in file-mapped areas.
Actually both patches are fixes for commit v2.6.33-5448-g6457474, because it was aimed at one scenario (singly used pages), but it breaks the logic in other scenarios (shared and/or executable pages)
> Pekka
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