Messages in this thread | | | Date | Thu, 22 Jan 2009 12:01:24 +0200 | Subject | Re: [patch] SLQB slab allocator | From | Pekka Enberg <> |
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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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