Re: [RFC v1 1/5] mm, slub: fix bulk alloc and free stats

Hyeonggon Yoo
2023-08-18T11:47:53Z

On Tue, Aug 8, 2023 at 6:53 PM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> The SLUB sysfs stats enabled CONFIG_SLUB_STATS have two deficiencies
> identified wrt bulk alloc/free operations:
>
> - Bulk allocations from cpu freelist are not counted. Add the
> ALLOC_FASTPATH counter there.
>
> - Bulk fastpath freeing will count a list of multiple objects with a
> single FREE_FASTPATH inc. Add a stat_add() variant to count them all.
>
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> mm/slub.c | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index e3b5d5c0eb3a..a9437d48840c 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -341,6 +341,14 @@ static inline void stat(const struct kmem_cache *s, enum stat_item si)
> #endif
> }
>
> +static inline void stat_add(const struct kmem_cache *s, enum stat_item si, int v)
> +{
> +#ifdef CONFIG_SLUB_STATS
> + raw_cpu_add(s->cpu_slab->stat[si], v);
> +#endif
> +}
> +
> +
> /*
> * Tracks for which NUMA nodes we have kmem_cache_nodes allocated.
> * Corresponds to node_state[N_NORMAL_MEMORY], but can temporarily
> @@ -3776,7 +3784,7 @@ static __always_inline void do_slab_free(struct kmem_cache *s,
>
> local_unlock(&s->cpu_slab->lock);
> }
> - stat(s, FREE_FASTPATH);
> + stat_add(s, FREE_FASTPATH, cnt);

Should bulk free slowpath also be counted in the same way?

> }
> #else /* CONFIG_SLUB_TINY */
> static void do_slab_free(struct kmem_cache *s,
> @@ -3978,6 +3986,7 @@ static inline int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags,
> c->freelist = get_freepointer(s, object);
> p[i] = object;
> maybe_wipe_obj_freeptr(s, p[i]);
> + stat(s, ALLOC_FASTPATH);
> }
> c->tid = next_tid(c->tid);
> local_unlock_irqrestore(&s->cpu_slab->lock, irqflags);
> --
> 2.41.0
>