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From: Suren Baghdasaryan <surenb@google.com>
Date: Fri, 15 Mar 2024 17:06:32 +0000
Message-ID: <CAJuCfpEsAHSAUP_EFP4yZdyZ1hfVPbQSWn9j-eZQdiRLy5MGYg@mail.gmail.com>
Subject: Re: [PATCH v5 23/37] mm/slab: add allocation accounting into slab
 allocation and free paths
To: Vlastimil Babka <vbabka@suse.cz>
Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, mhocko@suse.com, 
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On Fri, Mar 15, 2024 at 4:52=E2=80=AFPM Vlastimil Babka <vbabka@suse.cz> wr=
ote:
>
> On 3/15/24 16:43, Suren Baghdasaryan wrote:
> > On Fri, Mar 15, 2024 at 3:58=E2=80=AFAM Vlastimil Babka <vbabka@suse.cz=
> wrote:
> >>
> >> On 3/6/24 19:24, Suren Baghdasaryan wrote:
> >> > Account slab allocations using codetag reference embedded into slabo=
bj_ext.
> >> >
> >> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> >> > Co-developed-by: Kent Overstreet <kent.overstreet@linux.dev>
> >> > Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> >> > Reviewed-by: Kees Cook <keescook@chromium.org>
> >>
> >> Reviewed-by: Vlastimil Babka <vbabka@suse.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 =3D s->object_size;
> >> > +     struct slabobj_ext *obj_exts;
> >> >       bool kasan_init =3D init;
> >> >       size_t i;
> >> >       gfp_t init_flags =3D 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 =3D 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?

Yes, definitely. I was thinking about removing need_slab_obj_ext()
from prepare_slab_obj_exts_hook() and adding this instead of the above
code:

+        if (need_slab_obj_ext()) {
+                obj_exts =3D prepare_slab_obj_exts_hook(s, flags, p[i]);
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+                /*
+                 * Currently obj_exts is used only for allocation
profiling. If other users appear
+                 * then mem_alloc_profiling_enabled() check should be
added here.
+                 */
+                if (likely(obj_exts))
+                        alloc_tag_add(&obj_exts->ref,
current->alloc_tag, s->size);
+#endif
+        }

Does that look good?

> >> > +#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_t=
ag, s->size);
> >> > +#endif
> >>
> >> I think you could still do this a bit better:
> >>
> >> Check mem_alloc_profiling_enabled() once before the whole block callin=
g
> >> 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()=3D=3Dfalse. 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 sl=
ab *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, stru=
ct 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 fre=
elist
> >> >        * to remove objects, whose reuse must be delayed.
> >>
>
> --
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