On Sat, Nov 03, 2007 at 05:10:54PM +0000, Hugh Dickins wrote:
> 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 <[EMAIL PROTECTED]>
> ---
> I recommend this for 2.6.24-rc2 and 2.6.23-stable.
Hugh, you should also have CC'd linux-stable for this, otherwise there's
a risk that the patch remains unnoticed by the stable team (CC'd).
> 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;
> }
Regards,
Willy
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