Re: [PATCH v4 22/36] mm/slab: add allocation accounting into slab allocation and free paths

[Vlastimil Babka]

On 2/21/24 20:40, Suren Baghdasaryan wrote:
> Account slab allocations using codetag reference embedded into slabobj_ext.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Co-developed-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  mm/slab.h | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  mm/slub.c |  9 ++++++++
>  2 files changed, 75 insertions(+)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index 13b6ba2abd74..c4bd0d5348cb 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -567,6 +567,46 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
>  int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>  			gfp_t gfp, bool new_slab);
>  
> +static inline bool need_slab_obj_ext(void)
> +{
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> +	if (mem_alloc_profiling_enabled())
> +		return true;
> +#endif
> +	/*
> +	 * CONFIG_MEMCG_KMEM creates vector of obj_cgroup objects conditionally
> +	 * inside memcg_slab_post_alloc_hook. No other users for now.
> +	 */
> +	return false;
> +}
> +
> +static inline struct slabobj_ext *
> +prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
> +{
> +	struct slab *slab;
> +
> +	if (!p)
> +		return NULL;
> +
> +	if (!need_slab_obj_ext())
> +		return NULL;
> +
> +	if (s->flags & SLAB_NO_OBJ_EXT)
> +		return NULL;
> +
> +	if (flags & __GFP_NO_OBJ_EXT)
> +		return NULL;
> +
> +	slab = virt_to_slab(p);
> +	if (!slab_obj_exts(slab) &&
> +	    WARN(alloc_slab_obj_exts(slab, s, flags, false),
> +		 "%s, %s: Failed to create slab extension vector!\n",
> +		 __func__, s->name))
> +		return NULL;
> +
> +	return slab_obj_exts(slab) + obj_to_index(s, slab, p);
> +}
> +
>  #else /* CONFIG_SLAB_OBJ_EXT */
>  
>  static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
> @@ -589,6 +629,32 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
>  
>  #endif /* CONFIG_SLAB_OBJ_EXT */
>  
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> +
> +static inline void alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab,
> +					void **p, int objects)

Only used from mm/slub.c so could move?

> +{
> +	struct slabobj_ext *obj_exts;
> +	int i;
> +
> +	obj_exts = slab_obj_exts(slab);
> +	if (!obj_exts)
> +		return;
> +
> +	for (i = 0; i < objects; i++) {
> +		unsigned int off = obj_to_index(s, slab, p[i]);
> +
> +		alloc_tag_sub(&obj_exts[off].ref, s->size);
> +	}
> +}
> +
> +#else
> +
> +static inline void alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab,
> +					void **p, int objects) {}
> +
> +#endif /* CONFIG_MEM_ALLOC_PROFILING */
> +
>  #ifdef CONFIG_MEMCG_KMEM
>  void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
>  		     enum node_stat_item idx, int nr);
> diff --git a/mm/slub.c b/mm/slub.c
> index 5dc7beda6c0d..a69b6b4c8df6 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3826,6 +3826,7 @@ void slab_post_alloc_hook(struct kmem_cache *s,	struct obj_cgroup *objcg,
>  			  unsigned int orig_size)
>  {
>  	unsigned int zero_size = s->object_size;
> +	struct slabobj_ext *obj_exts;
>  	bool kasan_init = init;
>  	size_t i;
>  	gfp_t init_flags = flags & gfp_allowed_mask;
> @@ -3868,6 +3869,12 @@ void slab_post_alloc_hook(struct kmem_cache *s,	struct obj_cgroup *objcg,
>  		kmemleak_alloc_recursive(p[i], s->object_size, 1,
>  					 s->flags, init_flags);
>  		kmsan_slab_alloc(s, p[i], init_flags);
> +		obj_exts = prepare_slab_obj_exts_hook(s, flags, p[i]);
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> +		/* obj_exts can be allocated for other reasons */
> +		if (likely(obj_exts) && mem_alloc_profiling_enabled())
> +			alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
> +#endif

I think that like in the page allocator, this could be better guarded by
mem_alloc_profiling_enabled() as the outermost thing.

>  	}
>  
>  	memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
> @@ -4346,6 +4353,7 @@ void slab_free(struct kmem_cache *s, struct slab *slab, void *object,
>  	       unsigned long addr)
>  {
>  	memcg_slab_free_hook(s, slab, &object, 1);
> +	alloc_tagging_slab_free_hook(s, slab, &object, 1);

Same here, the static key is not even inside of this?

>  
>  	if (likely(slab_free_hook(s, object, slab_want_init_on_free(s))))
>  		do_slab_free(s, slab, object, object, 1, addr);
> @@ -4356,6 +4364,7 @@ void slab_free_bulk(struct kmem_cache *s, struct slab *slab, void *head,
>  		    void *tail, void **p, int cnt, unsigned long addr)
>  {
>  	memcg_slab_free_hook(s, slab, p, cnt);
> +	alloc_tagging_slab_free_hook(s, slab, p, cnt);

Ditto.

>  	/*
>  	 * With KASAN enabled slab_free_freelist_hook modifies the freelist
>  	 * to remove objects, whose reuse must be delayed.