Messages in this thread | | | Date | Mon, 8 Aug 2011 15:40:55 +0300 | Subject | Re: [PATCH 1/2] vmscan: promote shared file mapped pages | From | Pekka Enberg <> |
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On Mon, Aug 8, 2011 at 3:18 PM, Konstantin Khlebnikov <khlebnikov@parallels.com> wrote: > 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)
It'd be nice to have such details in the changelogs. FWIW,
Acked-by: Pekka Enberg <penberg@kernel.org> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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