Re: [PATCH] mm: memcg/slab: fix obj_cgroup_charge() return value handling

[Shakeel Butt <shakeelb@google.com>]

On Fri, Nov 27, 2020 at 8:18 AM Roman Gushchin <guro@fb.com> wrote:
>
> On Thu, Nov 26, 2020 at 09:55:24PM -0800, Shakeel Butt wrote:
> > On Thu, Nov 26, 2020 at 8:14 PM Roman Gushchin <guro@fb.com> wrote:
> > >
> > > Commit 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches
> > > for all allocations") introduced a regression into the handling of the
> > > obj_cgroup_charge() return value. If a non-zero value is returned
> > > (indicating of exceeding one of memory.max limits), the allocation
> > > should fail, instead of falling back to non-accounted mode.
> > >
> > > To make the code more readable, move memcg_slab_pre_alloc_hook()
> > > and memcg_slab_post_alloc_hook() calling conditions into bodies
> > > of these hooks.
> > >
> > > Fixes: 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations")
> > > Signed-off-by: Roman Gushchin <guro@fb.com>
> > > Cc: stable@vger.kernel.org
> > > ---
> > >  mm/slab.h | 40 ++++++++++++++++++++++++----------------
> > >  1 file changed, 24 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/mm/slab.h b/mm/slab.h
> > > index 59aeb0d9f11b..5dc89d8fb05e 100644
> > > --- a/mm/slab.h
> > > +++ b/mm/slab.h
> > > @@ -257,22 +257,32 @@ static inline size_t obj_full_size(struct kmem_cache *s)
> > >         return s->size + sizeof(struct obj_cgroup *);
> > >  }
> > >
> > > -static inline struct obj_cgroup *memcg_slab_pre_alloc_hook(struct kmem_cache *s,
> > > -                                                          size_t objects,
> > > -                                                          gfp_t flags)
> > > +/*
> > > + * Returns true if the allocation should fail.
> >
> > IMO returning false if the allocation should fail makes this more
> > clear. Otherwise the patch looks good to me.
>
> Ok, I agree. Here is an updated version.
>
> Thank you for looking in!
>
> --
>
> From 456ce03f1c91baf5e2441dce0649e09617437fe4 Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <guro@fb.com>
> Date: Thu, 26 Nov 2020 07:39:57 -0800
> Subject: [PATCH v2] mm: memcg/slab: fix obj_cgroup_charge() return value
>  handling
>
> Commit 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches
> for all allocations") introduced a regression into the handling of the
> obj_cgroup_charge() return value. If a non-zero value is returned
> (indicating of exceeding one of memory.max limits), the allocation
> should fail, instead of falling back to non-accounted mode.
>
> To make the code more readable, move memcg_slab_pre_alloc_hook()
> and memcg_slab_post_alloc_hook() calling conditions into bodies
> of these hooks.
>
> Fixes: 10befea91b61 ("mm: memcg/slab: use a single set of kmem_caches for all allocations")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: stable@vger.kernel.org

Reviewed-by: Shakeel Butt <shakeelb@google.com>