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    Subject[PATCH 1/2] slub: fix leakage
    Slub has been quite leaky under load.  Taking mm_struct as an example, in
    a loop of swapping kernel builds, after the first iteration slabinfo shows:
    Name Objects Objsize Space Slabs/Part/Cpu O/S O %Fr %Ef Flg
    mm_struct 55 840 73.7K 18/7/4 4 0 38 62 A
    but Objects and Partials steadily creep up - after the 340th iteration:
    mm_struct 110 840 188.4K 46/36/4 4 0 78 49 A

    The culprit turns out to be __slab_alloc(), where it copes with the race
    that another task has assigned the cpu slab while we were allocating one.
    Don't rush off to load_freelist there: that assumes c->freelist is empty,
    and will lose all of its free slots when c->page->freelist is not empty.
    Instead just do a local allocation from c->freelist when it has one.

    Which fixes the leakage: Objects and Partials then remain stable.

    Signed-off-by: Hugh Dickins <hugh@veritas.com>
    ---
    I recommend this for 2.6.24-rc2 and 2.6.23-stable.

    mm/slub.c | 5 +++++
    1 file changed, 5 insertions(+)

    --- 2.6.24-rc1/mm/slub.c 2007-10-24 07:16:04.000000000 +0100
    +++ linux/mm/slub.c 2007-11-03 13:22:31.000000000 +0000
    @@ -1525,6 +1525,11 @@ new_slab:
    * want the current one since its cache hot
    */
    discard_slab(s, new);
    + if (c->freelist) {
    + object = c->freelist;
    + c->freelist = object[c->offset];
    + return object;
    + }
    slab_lock(c->page);
    goto load_freelist;
    }
    -
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