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    SubjectRe: O_DIRECT question
    On 1/11/07, Nick Piggin <nickpiggin@yahoo.com.au> wrote:
    > Andrew Morton wrote:
    > > On Thu, 11 Jan 2007 14:45:12 +0800
    > > Aubrey <aubreylee@gmail.com> wrote:
    > >
    > >
    > >>>In the interim you could do the old "echo 3 > /proc/sys/vm/drop_caches"
    > >>>thing, but that's terribly crude - drop_caches is really only for debugging
    > >>>and benchmarking.
    > >>>
    > >>
    > >>Yes. This method can drop caches, but will fragment memory.
    > >
    > >
    > > That's what page reclaim will do as well.
    > >
    > > What you want is Mel's antifragmentation work, or lumpy reclaim.
    > >
    > >
    > >>This is
    > >>not what I want. I want cache is limited to a tunable value of the
    > >>whole memory. For example, if total memory is 128M, is there a way to
    > >>trigger reclaim when cache size > 16M?
    > >
    > >
    > > If there was, it'd "fragment memory" as well.
    > >
    > > You might get a little benefit from increasing /proc/sys/vm/min_free_kbytes,
    > > but not much. Some page allocation tweaks would aid that.
    > >
    > > But basically, to do this well, serious work is needed.
    >
    > OTOH, the antifragmentation stuff can also break down eventually,
    > especially if higher order allocations are actually in common use.

    That's right. When VFS cache eat up almost all of the memory, I think
    no memory algorithm can help the case, including Mei's anti-fragment
    patch.

    >
    > What you _really_ want to do is avoid large mallocs after boot, or use
    > a CPU with an mmu. I don't think nommu linux was ever intended to be a
    > simple drop in replacement for a normal unix kernel.

    Is there a position available working on mmu CPU? Joking, :)
    Yes, some problems are serious on nommu linux. But I think we should
    try to fix them not avoid them.

    -Aubrey
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