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 08:43:53 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
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Subject: Re: [PATCH v5 23/37] mm/slab: add allocation accounting into slab
 allocation and free paths

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())
> > +                     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.
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.
>