linux-kernel - Re: [PATCH v5 23/37] mm/slab: add allocation accounting into slab allocation and free paths

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Date: Fri, 15 Mar 2024 17:52:50 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH v5 23/37] mm/slab: add allocation accounting into slab
 allocation and free paths

On 3/15/24 16:43, Suren Baghdasaryan wrote:
> On Fri, Mar 15, 2024 at 3:58 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>
>> On 3/6/24 19:24, Suren Baghdasaryan wrote:
>> > Account slab allocations using codetag reference embedded into slabobj_ext.
>> >
>> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
>> > Co-developed-by: Kent Overstreet <kent.overstreet@...ux.dev>
>> > Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
>> > Reviewed-by: Kees Cook <keescook@...omium.org>
>>
>> Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
>>
>> Nit below:
>>
>> > @@ -3833,6 +3913,7 @@ 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;
>> > @@ -3875,6 +3956,12 @@ 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())

Could you at least flip these two checks then so the static key one goes first?

>> > +                     alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size);
>> > +#endif
>>
>> I think you could still do this a bit better:
>>
>> Check mem_alloc_profiling_enabled() once before the whole block calling
>> prepare_slab_obj_exts_hook() and alloc_tag_add()
>> Remove need_slab_obj_ext() check from prepare_slab_obj_exts_hook()
> 
> Agree about checking mem_alloc_profiling_enabled() early and one time,
> except I would like to use need_slab_obj_ext() instead of
> mem_alloc_profiling_enabled() for that check. Currently they are
> equivalent but if there are more slab_obj_ext users in the future then
> there will be cases when we need to prepare_slab_obj_exts_hook() even
> when mem_alloc_profiling_enabled()==false. need_slab_obj_ext() will be
> easy to extend for such cases.

I thought we don't generally future-proof internal implementation details
like this until it's actually needed. But at least what I suggested above
would help, thanks.

> Thanks,
> Suren.
> 
>>
>> >       }
>> >
>> >       memcg_slab_post_alloc_hook(s, objcg, flags, size, p);
>> > @@ -4353,6 +4440,7 @@ 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);
>> >
>> >       if (likely(slab_free_hook(s, object, slab_want_init_on_free(s))))
>> >               do_slab_free(s, slab, object, object, 1, addr);
>> > @@ -4363,6 +4451,7 @@ 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);
>> >       /*
>> >        * With KASAN enabled slab_free_freelist_hook modifies the freelist
>> >        * to remove objects, whose reuse must be delayed.
>>