Re: [PATCH v3 1/2] mm, slab: add an optimistic __slab_try_return_freelist()

[Harry Yoo <harry@kernel.org>]

On 5/22/26 11:23 PM, Vlastimil Babka (SUSE) wrote:
> When we end up returning extraneous objects during refill to a slab
> where we just did a get_freelist_nofreeze(), it is likely no other CPU
> has freed objects to it meanwhile. We can then reattach the remainder of
> the freelist without having to walk the (potentially cache cold)
> freelist for finding its tail to connect slab->freelist to it.
>
> Add a __slab_try_return_freelist() function that does that. As suggested
> by Hao Li, it doesn't need to also return the slab to the partial list,
> because there's code in __refill_objects_node() that already does that
> for any slabs where we don't detach the freelist in the first place. So
> we just put the slab back to the pc.slabs list. It's no longer likely
> that the list will be empty now, so remove the unlikely() annotation.
>
> However, also change that code to add to the tail of the partial list
> instead of head to match what __slab_free() did and avoid a regression,
> that was reported for the earlier version by the kernel test robot [1].
> This change will also affect slabs which were grabbed from the partial
> list and not refilled from even partially, but those should be much more
> rare than a partial refill.
>
> [1]https://lore.kernel.org/all/202605112204.9382cecf-lkp@intel.com/
>
> Reviewed-by: Hao Li<hao.li@linux.dev>
> Signed-off-by: Vlastimil Babka (SUSE)<vbabka@kernel.org>
> ---

Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>

-- 
Cheers,
Harry / Hyeonggon