Re: [PATCH 1/2] vmscan: promote shared file mapped pages

[Konstantin Khlebnikov]

Pekka Enberg wrote:
> Hi Konstantin,
>
> On Mon, Aug 8, 2011 at 2:06 PM, Konstantin Khlebnikov
> <khlebnikov@xxxxxxxxxx>  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@xxxxxxxxxx>
>
> 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/