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    SubjectRe: 2.6.23-rc1-mm2 (vm-dont-run-touch_buffer-during-buffercache-lookups.patch)
    On Wed, 01 Aug 2007 03:36:30 -0400 Eric St-Laurent <> wrote:

    > On Tue, 2007-31-07 at 23:09 -0700, Andrew Morton wrote:
    > > +vm-dont-run-touch_buffer-during-buffercache-lookups.patch
    > >
    > > A little VM experiment. See changelog for details.
    > > We don't have any tests to determine the effects of this, and nobody will
    > > bother setting one up, so ho hum, this remains in -mm for ever.
    > > I don't think there's any point in doing this until we have some decent
    > > testcases.
    > Hi Andrew,
    > For which problem this patch was coded?

    Good question. I think the current behaviour is just wrong. What the
    effect of changing it will be is hard to predict - probably little.

    > Is it a potential fix to the
    > updatedb problem?

    That's one workload which is particularly susceptible to the problemn which
    that patch addresses, yes. But in my (brief) testing it didn't make musch

    > Is the patch effective without the filesystem dependant change you talk
    > about? (I use reiserfs)

    Yes, it'll work as designed with reiserfs.

    > I've been thinking about a test case for the updatedb problem:
    > 1. Script or program that create a large number of directories and zero
    > sized files. Same setup for everyone to have reproducible results.
    > 2. Run updatedb on those.
    > 3. Observe the effects (with vmstat, slabinfo and meminfo) before,
    > during and after the updatedb run.
    > 4. Do something to trigger some reclaim like copying a large file.
    > 5. See the effects.
    > What do you think? What would be the ideal test case for the problem in
    > your opinion?

    Sounds good, yes.

    Or you could do something more real-worldly like start up OO, firefox and
    friends, then run /etc/cron.daily/everything and see what the
    before-and-after effects are. The aggregate info we're looking for is
    captured in /proc/meminfo: swapped, Mapped, Cached, Buffers.

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