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    SubjectRe: BC: resource beancounters (v2)
    On Fri, 25 Aug 2006 20:30:26 +0400
    Andrey Savochkin <> wrote:

    > On Fri, Aug 25, 2006 at 07:30:03AM -0700, Andrew Morton wrote:
    > >
    > > D) Virtual scan of mm's in the over-limit container
    > >
    > > E) Modify existing physical scanner to be able to skip pages which
    > > belong to not-over-limit containers.
    > I've actually tried (E), but it didn't work as I wished.
    > It didn't handle well shared pages.
    > Then, in my experiments such modified scanner was unable to regulate
    > quality-of-service. When I ran 2 over-the-limit containers, they worked
    > equally slow regardless of their limits and work set size.
    > That is, I didn't observe a smooth transition "under limit, maximum
    > performance" to "slightly over limit, a bit reduced performance" to
    > "significantly over limit, poor performance". Neither did I see any fairness
    > in how containers got penalized for exceeding their limits.
    > My explanation of what I observed is that
    > - since filesystem caches play a huge role in performance, page scanner will
    > be very limited in controlling container's performance if caches
    > stay shared between containers,
    > - in the absence of decent disk I/O manager, stalls due to swapin/swapout
    > are more influenced by disk subsystem than by page scanner policy.
    > So in fact modified page scanner provides control over memory usage only as
    > "stay under limits or die", and doesn't show many advantages over (B) or (C).
    > At the same time, skipping pages visibly penalizes "good citizens", not only
    > in disk bandwidth but in CPU overhead as well.
    > So I settled for (A)-(C) for now.
    > But it certainly would be interesting to hear if someone else makes such
    > experiments.

    Makes sense. If one is looking for good machine partitioning then a shared
    disk is obviously a great contention point. To address that we'd need to
    be able to say "container A swaps to /dev/sda1 and container B swaps to
    /dev/sdb1". But the swap system at present can't do that.

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