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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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