linux-kernel - Re: [PATCH v3 21/35] mm/slab: add allocation accounting into slab allocation and free paths

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Date: Fri, 16 Feb 2024 09:11:17 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org, mhocko@...e.com, 
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Subject: Re: [PATCH v3 21/35] mm/slab: add allocation accounting into slab
 allocation and free paths

On Fri, Feb 16, 2024 at 8:39 AM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> On Fri, Feb 16, 2024 at 05:31:11PM +0100, Vlastimil Babka wrote:
> > On 2/12/24 22:39, 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>
> > > ---
> > >  mm/slab.h | 26 ++++++++++++++++++++++++++
> > >  mm/slub.c |  5 +++++
> > >  2 files changed, 31 insertions(+)
> > >
> > > diff --git a/mm/slab.h b/mm/slab.h
> > > index 224a4b2305fb..c4bd0d5348cb 100644
> > > --- a/mm/slab.h
> > > +++ b/mm/slab.h
> > > @@ -629,6 +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)
> > > +{
> > > +   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 */
> >
> > You don't actually use the alloc_tagging_slab_free_hook() anywhere? I see
> > it's in the next patch, but logically should belong to this one.
>
> I don't think it makes any sense to quibble about introducing something
> in one patch that's not used until the next patch; often times, it's
> just easier to review that way.

Yeah, there were several cases where I was debating with myself which
way to split a patch (same was, as you noticed, with
prepare_slab_obj_exts_hook()). Since we already moved
prepare_slab_obj_exts_hook(), alloc_tagging_slab_free_hook() will
probably move into the same patch. I'll go over the results once more
to see if the new split makes more sense, if not will keep it here.
Thanks!