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List-Subscribe: List-Unsubscribe: On Mon, Dec 15, 2025 at 03:30:48PM +0100, Vlastimil Babka wrote: > On 12/10/25 01:26, Hao Li wrote: > > From: Hao Li > > > > When __pcs_replace_empty_main() fails to obtain a full sheaf directly > > from the barn, it may either: > > > > - Refill an empty sheaf obtained via barn_get_empty_sheaf(), or > > - Allocate a brand new full sheaf via alloc_full_sheaf(). > > > > After reacquiring the per-CPU lock, if pcs->main is still empty and > > pcs->spare is NULL, the current code donates the empty main sheaf to > > the barn via barn_put_empty_sheaf() and installs the full sheaf as > > pcs->main, leaving pcs->spare unpopulated. > > > > Instead, keep the existing empty main sheaf locally as the spare: > > > > pcs->spare = pcs->main; > > pcs->main = full; > > > > This populates pcs->spare earlier, which can reduce future barn traffic. > > > > Suggested-by: Vlastimil Babka > > Signed-off-by: Hao Li > > --- > > > > The Gmail account(haoli.tcs) I used to send v1 of the patch has been > > restricted from sending emails for unknown reasons, so I'm sending v2 > > from this address instead. Thanks. > > > > mm/slub.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/mm/slub.c b/mm/slub.c > > index a0b905c2a557..a3e73ebb0cc8 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -5077,6 +5077,11 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, > > */ > > > > if (pcs->main->size == 0) { > > + if (!pcs->spare) { > > + pcs->spare = pcs->main; > > + pcs->main = full; > > + return pcs; > > + } > > barn_put_empty_sheaf(barn, pcs->main); > > pcs->main = full; > > return pcs; > > Thanks, LGTM. We can make it smaller though. Adding to slab/for-next > adjusted like this: > > diff --git a/mm/slub.c b/mm/slub.c > index f21b2f0c6f5a..ad71f01571f0 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5052,7 +5052,11 @@ __pcs_replace_empty_main(struct kmem_cache *s, struct slub_percpu_sheaves *pcs, > */ > > if (pcs->main->size == 0) { > - barn_put_empty_sheaf(barn, pcs->main); > + if (!pcs->spare) { > + pcs->spare = pcs->main; > + } else { > + barn_put_empty_sheaf(barn, pcs->main); > + } nit: no braces for single statement? > pcs->main = full; > return pcs; > } Otherwise LGTM, so: Reviewed-by: Harry Yoo -- Cheers, Harry / Hyeonggon