On 1/23/24 10:33, Chengming Zhou wrote:
> The likely case is that we get a usable slab from the cpu partial list,
> we can directly load freelist from it and return back, instead of going
> the other way that need more work, like reenable interrupt and recheck.
>
> But we need to remove the "VM_BUG_ON(!new.frozen)" in get_freelist()
> for reusing it, since cpu partial slab is not frozen. It seems
> acceptable since it's only for debug purpose.
>
> And get_freelist() also assumes it can return NULL if the freelist is
> empty, which is not possible for the cpu partial slab case, so we
> add "VM_BUG_ON(!freelist)" after get_freelist() to make it explicit.
>
> There is some small performance improvement too, which shows by:
> perf bench sched messaging -g 5 -t -l 100000
>
> mm-stable slub-optimize
> Total time 7.473 7.209
>
> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
I'm including the series to slab/for-6.9/optimize-get-freelist and
slab/for-next, thanks!
> ---
> mm/slub.c | 21 +++++++++++----------
> 1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 2ef88bbf56a3..fda402b2d649 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3326,7 +3326,6 @@ static inline void *get_freelist(struct kmem_cache *s, struct slab *slab)
> counters = slab->counters;
>
> new.counters = counters;
> - VM_BUG_ON(!new.frozen);
>
> new.inuse = slab->objects;
> new.frozen = freelist != NULL;
> @@ -3498,18 +3497,20 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
>
> slab = slub_percpu_partial(c);
> slub_set_percpu_partial(c, slab);
> - local_unlock_irqrestore(&s->cpu_slab->lock, flags);
> - stat(s, CPU_PARTIAL_ALLOC);
>
> - if (unlikely(!node_match(slab, node) ||
> - !pfmemalloc_match(slab, gfpflags))) {
> - slab->next = NULL;
> - __put_partials(s, slab);
> - continue;
> + if (likely(node_match(slab, node) &&
> + pfmemalloc_match(slab, gfpflags))) {
> + c->slab = slab;
> + freelist = get_freelist(s, slab);
> + VM_BUG_ON(!freelist);
> + stat(s, CPU_PARTIAL_ALLOC);
> + goto load_freelist;
> }
>
> - freelist = freeze_slab(s, slab);
> - goto retry_load_slab;
> + local_unlock_irqrestore(&s->cpu_slab->lock, flags);
> +
> + slab->next = NULL;
> + __put_partials(s, slab);
> }
> #endif
>
>
