On 3/31/24 4:19 AM, xiongwei.song@xxxxxxxxxxxxx wrote:
> From: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
>
> The break conditions can be more readable and simple.
>
> We can check if we need to fill cpu partial after getting the first
> partial slab. If kmem_cache_has_cpu_partial() returns true, we fill
> cpu partial from next iteration, or break up the loop.
>
> Then we can remove the preprocessor condition of
> CONFIG_SLUB_CPU_PARTIAL. Use dummy slub_get_cpu_partial() to make
> compiler silent.
>
> Signed-off-by: Xiongwei Song <xiongwei.song@xxxxxxxxxxxxx>
> ---
> mm/slub.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 590cc953895d..ec91c7435d4e 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2614,18 +2614,20 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> if (!partial) {
> partial = slab;
> stat(s, ALLOC_FROM_PARTIAL);
> - } else {
> - put_cpu_partial(s, slab, 0);
> - stat(s, CPU_PARTIAL_NODE);
> - partial_slabs++;
> +
> + /* Fill cpu partial if needed from next iteration, or break */
> + if (kmem_cache_has_cpu_partial(s))
That kinda puts back the check removed in patch 1, although only in the
first iteration. Still not ideal.
> + continue;
> + else
> + break;
> }
> -#ifdef CONFIG_SLUB_CPU_PARTIAL
> - if (partial_slabs > s->cpu_partial_slabs / 2)
> - break;
> -#else
> - break;
> -#endif
I'd suggest intead of the changes done in this patch, only change this part
above to:
if ((slub_get_cpu_partial(s) == 0) ||
(partial_slabs > slub_get_cpu_partial(s) / 2))
break;
That gets rid of the #ifdef and also fixes a weird corner case that if we
set cpu_partial_slabs to 0 from sysfs, we still allocate at least one here.
It could be tempting to use >= instead of > to achieve the same effect but
that would have unintended performance effects that would best be evaluated
separately.
>
> + put_cpu_partial(s, slab, 0);
> + stat(s, CPU_PARTIAL_NODE);
> + partial_slabs++;
> +
> + if (partial_slabs > slub_get_cpu_partial(s) / 2)
> + break;
> }
> spin_unlock_irqrestore(&n->list_lock, flags);
> return partial;
