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1/29/26 10:30, Harry Yoo wrote: > > On Thu, Jan 29, 2026 at 05:21:21PM +0800, Hao Li wrote: > >> On Thu, Jan 29, 2026 at 10:07:57AM +0100, Vlastimil Babka wrote: > >> > Kernel test robot has reported a regression in the patch "slab: refill > >> > sheaves from all nodes". When taken in isolation like this, there is > >> > indeed a tradeoff - we prefer to use remote objects prior to allocating > >> > new local slabs. It is replicating a behavior that existed before > >> > sheaves for replenishing cpu (partial) slabs - now called > >> > get_from_any_partial() to allocate a single object. > >> > > >> > So the possibility of allocating remote objects is intended even if > >> > remote accesses are then slower. But the profiles in the report also > >> > suggested a contention on the list_lock spinlock. And that's something > >> > we can try to avoid without much tradeoff - if someone else has the > >> > spin_lock, it's more likely they are allocating from the node than > >> > freeing to it, so we can skip it even if it means allocating a new local > >> > slab - contributing to that lock's contention isn't worth it. It should > >> > not result in partial slabs accumulating on the remote node. > >> > > >> > Thus add an allow_spin parameter to __refill_objects_node() and > >> > get_partial_node_bulk() to make the attempts from __refill_objects_any() > >> > use only a trylock. > >> > > >> > Reported-by: kernel test robot > >> > Link: https://lore.kernel.org/oe-lkp/202601132136.77efd6d7-lkp@intel.com > >> > Signed-off-by: Vlastimil Babka > >> > >> In my testing, this patch improved performance by: > >> > >> will-it-scale.64.processes +14.2% > >> will-it-scale.128.processes +9.6% > >> will-it-scale.192.processes +10.8% > >> will-it-scale.per_process_ops +11.6% > >> > >> Tested-by: Hao Li > > > > I wonder if using spin_is_contended() or spin_is_locked() > > would be better than trylock by avoiding an atomic operation? > > I checked and found that spin_trylock() itself implements a non-atomic check > before the atomic. So adding a spin_is_locked() would only help the caller > bail out a bit faster, but this is not a fastpath. It wouldn't help the > cache coherency traffic, AFAIU. I looked at qspinlock version of spin_trylock() and you're right :) I just assumed it will always do a CAS but it's not the case! -- Cheers, Harry / Hyeonggon