linux-kernel - Re: [PATCH v3 08/35] mm: prevent slabobj_ext allocations for slabobj_ext and kmem

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Date: Thu, 15 Feb 2024 14:13:17 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
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Subject: Re: [PATCH v3 08/35] mm: prevent slabobj_ext allocations for
 slabobj_ext and kmem_cache objects

On Thu, Feb 15, 2024 at 1:44 PM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 2/12/24 22:38, Suren Baghdasaryan wrote:
> > Use __GFP_NO_OBJ_EXT to prevent recursions when allocating slabobj_ext
> > objects. Also prevent slabobj_ext allocations for kmem_cache objects.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > ---
> >  mm/slab.h        | 6 ++++++
> >  mm/slab_common.c | 2 ++
> >  2 files changed, 8 insertions(+)
> >
> > diff --git a/mm/slab.h b/mm/slab.h
> > index 436a126486b5..f4ff635091e4 100644
> > --- a/mm/slab.h
> > +++ b/mm/slab.h
> > @@ -589,6 +589,12 @@ prepare_slab_obj_exts_hook(struct kmem_cache *s, gfp_t flags, void *p)
> >       if (!need_slab_obj_ext())
> >               return NULL;
> >
> > +     if (s->flags & SLAB_NO_OBJ_EXT)
> > +             return NULL;
> > +
> > +     if (flags & __GFP_NO_OBJ_EXT)
> > +             return NULL;
>
> Since we agreed to postpone this function, when it appears later it can have
> those in.

Yes, I think that works. Will have this in the same patch.

>
> >       slab = virt_to_slab(p);
> >       if (!slab_obj_exts(slab) &&
> >           WARN(alloc_slab_obj_exts(slab, s, flags, false),
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 6bfa1810da5e..83fec2dd2e2d 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -218,6 +218,8 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> >       void *vec;
> >
> >       gfp &= ~OBJCGS_CLEAR_MASK;
> > +     /* Prevent recursive extension vector allocation */
> > +     gfp |= __GFP_NO_OBJ_EXT;
>
> And this could become part of 6/35 mm: introduce __GFP_NO_OBJ_EXT ... ?

Yes, that will eliminate this patch. Thanks!

>
> >       vec = kcalloc_node(objects, sizeof(struct slabobj_ext), gfp,
> >                          slab_nid(slab));
> >       if (!vec)
>