Re: [PATCH v4 07/36] mm: introduce slabobj_ext to support slab object extensions

Vlastimil Babka
2024-02-26T16:26:28Z

On 2/21/24 20:40, Suren Baghdasaryan wrote:
> Currently slab pages can store only vectors of obj_cgroup pointers in
> page->memcg_data. Introduce slabobj_ext structure to allow more data
> to be stored for each slab object. Wrap obj_cgroup into slabobj_ext
> to support current functionality while allowing to extend slabobj_ext
> in the future.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

Hi, mostly good from slab perspective, just some fixups:

> --- a/mm/slab.h
> +++ b/mm/slab.h
> -int memcg_alloc_slab_cgroups(struct slab *slab, struct kmem_cache *s,
> - gfp_t gfp, bool new_slab);
> -void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
> - enum node_stat_item idx, int nr);
> -#else /* CONFIG_MEMCG_KMEM */
> -static inline struct obj_cgroup **slab_objcgs(struct slab *slab)
> +int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> + gfp_t gfp, bool new_slab);
>

We could remove this declaration and make the function static in mm/slub.c.

> +#else /* CONFIG_SLAB_OBJ_EXT */
> +
> +static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
> {
> return NULL;
> }
>
> -static inline int memcg_alloc_slab_cgroups(struct slab *slab,
> - struct kmem_cache *s, gfp_t gfp,
> - bool new_slab)
> +static inline int alloc_slab_obj_exts(struct slab *slab,
> + struct kmem_cache *s, gfp_t gfp,
> + bool new_slab)
> {
> return 0;
> }

Ditto

> -#endif /* CONFIG_MEMCG_KMEM */
> +
> +static inline struct slabobj_ext *
> +prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
> +{
> + return NULL;
> +}

Same here (and the definition and usage even happens in later patch).

> +#endif /* CONFIG_SLAB_OBJ_EXT */
> +
> +#ifdef CONFIG_MEMCG_KMEM
> +void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
> + enum node_stat_item idx, int nr);
> +#endif
>
> size_t __ksize(const void *objp);
>
> diff --git a/mm/slub.c b/mm/slub.c
> index d31b03a8d9d5..76fb600fbc80 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -683,10 +683,10 @@ static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *sla
>
> if (s->flags & __CMPXCHG_DOUBLE) {
> ret = __update_freelist_fast(slab, freelist_old, counters_old,
> - freelist_new, counters_new);
> + freelist_new, counters_new);
> } else {
> ret = __update_freelist_slow(slab, freelist_old, counters_old,
> - freelist_new, counters_new);
> + freelist_new, counters_new);
> }
> if (likely(ret))
> return true;
> @@ -710,13 +710,13 @@ static inline bool slab_update_freelist(struct kmem_cache *s, struct slab *slab,
>
> if (s->flags & __CMPXCHG_DOUBLE) {
> ret = __update_freelist_fast(slab, freelist_old, counters_old,
> - freelist_new, counters_new);
> + freelist_new, counters_new);
> } else {
> unsigned long flags;
>
> local_irq_save(flags);
> ret = __update_freelist_slow(slab, freelist_old, counters_old,
> - freelist_new, counters_new);
> + freelist_new, counters_new);

Please no drive-by fixups of whitespace in code you're not actually
changing. I thought you agreed in v3?

> static inline bool memcg_slab_pre_alloc_hook(struct kmem_cache *s,
> struct list_lru *lru,
> struct obj_cgroup **objcgp,
> @@ -2314,7 +2364,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
> struct kmem_cache *s, gfp_t gfp)
> {
> if (memcg_kmem_online() && (s->flags & SLAB_ACCOUNT))
> - memcg_alloc_slab_cgroups(slab, s, gfp, true);
> + alloc_slab_obj_exts(slab, s, gfp, true);

This is still guarded by the memcg_kmem_online() static key, which is good.

>
> mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
> PAGE_SIZE << order);
> @@ -2323,8 +2373,7 @@ static __always_inline void account_slab(struct slab *slab, int order,
> static __always_inline void unaccount_slab(struct slab *slab, int order,
> struct kmem_cache *s)
> {
> - if (memcg_kmem_online())
> - memcg_free_slab_cgroups(slab);
> + free_slab_obj_exts(slab);

But this no longer is, yet it still could be?

>
> mod_node_page_state(slab_pgdat(slab), cache_vmstat_idx(s),
> -(PAGE_SIZE << order));