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    SubjectRe: [patch] SLQB slab allocator
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    Hi Hugh,

    On Wed, Jan 21, 2009 at 8:10 PM, Hugh Dickins <hugh@veritas.com> wrote:
    > I was initially _very_ impressed by how well it did on my venerable
    > tmpfs loop swapping loads, where I'd expected next to no effect; but
    > that turned out to be because on three machines I'd been using SLUB,
    > without remembering how default slub_max_order got raised from 1 to 3
    > in 2.6.26 (hmm, and Documentation/vm/slub.txt not updated).
    >
    > That's been making SLUB behave pretty badly (e.g. elapsed time 30%
    > more than SLAB) with swapping loads on most of my machines. Though
    > oddly one seems immune, and another takes four times as long: guess
    > it depends on how close to thrashing, but probably more to investigate
    > there. I think my original SLUB versus SLAB comparisons were done on
    > the immune one: as I remember, SLUB and SLAB were equivalent on those
    > loads when SLUB came in, but even with boot option slub_max_order=1,
    > SLUB is still slower than SLAB on such tests (e.g. 2% slower).
    > FWIW - swapping loads are not what anybody should tune for.

    What kind of machine are you seeing this on? It sounds like it could
    be a side-effect from commit 9b2cd506e5f2117f94c28a0040bf5da058105316
    ("slub: Calculate min_objects based on number of processors").

    Pekka


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