Optimizes the current refill leftover handling in a way that should have
no downsides, so we have a better baseline for any further changes (e.g.
spilling or caching the leftover) that involve some tradeoffs.

It's based on slab/for-7.2/perf without the previous version of the
first patch. Sending a new version due to accumulated fixups to the
first patch that resolve a perf regression, and a new cleanup patch on
top.

Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
---
Changes in v3:
- Fixup patch 1 to resolve lkp regression https://lore.kernel.org/all/202605112204.9382cecf-lkp@intel.com/
  - Return slabs to tail of the partial list - this resolved the
    regression.
  - Remove an unlikely() - this had no effect but it's factually
    correct.
- Add patch 2 wich further changes created by trying to resolve the
  regression. Those had no effect but still makes sense as a code
  simplification.
- Link to v2: https://patch.msgid.link/20260427-b4-refill-optimistic-return-v2-1-1672467a792d@kernel.org

Changes in v2:
- rebase to slab/for-7.2/perf, drop RFC
- simplify to reuse the existing reattaching to partial list (Hao Li)
- Add R-b from Hao Li, thanks!
- drop the stat items - they serverd to verify the optimistic path was
  succeeding, but are too detailed for mainline
- Link to v1: https://patch.msgid.link/20260421-b4-refill-optimistic-return-v1-1-24f0bfc1acff@kernel.org

---
Vlastimil Babka (SUSE) (2):
      mm, slab: add an optimistic __slab_try_return_freelist()
      mm, slab: simplify returning slab in __refill_objects_node()

 mm/slub.c | 69 ++++++++++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 48 insertions(+), 21 deletions(-)
---
base-commit: dc795d4c0282a4fbfbcd76a70c09ca0888678443
change-id: 20260421-b4-refill-optimistic-return-f44d3b74cc49

Best regards,
--  
Vlastimil Babka (SUSE) <vbabka@kernel.org>