Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20200614123923.99189-1-songmuchun@bytedance.com>
 <20200614123923.99189-4-songmuchun@bytedance.com> <CAAmzW4N1DRBxsMAX2a_jxUW10vOwW1VsGj8ztuvvWT4NB3Ocnw@mail.gmail.com>
 <CAMZfGtUQ+0w=n9YSQjQc1uwJFJrvtfj=rcTnNYnewCPiHmDLEw@mail.gmail.com>
In-Reply-To: <CAMZfGtUQ+0w=n9YSQjQc1uwJFJrvtfj=rcTnNYnewCPiHmDLEw@mail.gmail.com>
From:   Joonsoo Kim <js1304@gmail.com>
Date:   Mon, 15 Jun 2020 16:25:02 +0900
Message-ID: <CAAmzW4N=Rq5qc60DA9-ombrzOxaKEnKUFXM6_DJfq=5bCRdO=g@mail.gmail.com>
Subject: Re: [External] Re: [PATCH 3/3] mm/slub: Fix release all resources
 used by a slab cache
To:     Muchun Song <songmuchun@bytedance.com>
Cc:     Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

2020=EB=85=84 6=EC=9B=94 15=EC=9D=BC (=EC=9B=94) =EC=98=A4=ED=9B=84 3:41, M=
uchun Song <songmuchun@bytedance.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Mon, Jun 15, 2020 at 2:23 PM Joonsoo Kim <js1304@gmail.com> wrote:
> >
> > 2020=EB=85=84 6=EC=9B=94 14=EC=9D=BC (=EC=9D=BC) =EC=98=A4=ED=9B=84 9:3=
9, Muchun Song <songmuchun@bytedance.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=
=B1:
> > >
> > > The function of __kmem_cache_shutdown() is that release all resources
> > > used by the slab cache, while currently it stop release resources whe=
n
> > > the preceding node is not empty.
> > >
> > > Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> > > ---
> > >  mm/slub.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index b73505df3de2..4e477ef0f2b9 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -3839,6 +3839,7 @@ bool __kmem_cache_empty(struct kmem_cache *s)
> > >   */
> > >  int __kmem_cache_shutdown(struct kmem_cache *s)
> > >  {
> > > +       int ret =3D 0;
> > >         int node;
> > >         struct kmem_cache_node *n;
> > >
> > > @@ -3846,11 +3847,11 @@ int __kmem_cache_shutdown(struct kmem_cache *=
s)
> > >         /* Attempt to free all objects */
> > >         for_each_kmem_cache_node(s, node, n) {
> > >                 free_partial(s, n);
> > > -               if (node_nr_slabs(n))
> > > -                       return 1;
> > > +               if (!ret && node_nr_slabs(n))
> > > +                       ret =3D 1;
> > >         }
> >
> > I don't think that this is an improvement.
> >
> > If the shutdown condition isn't met, we don't need to process further.
> > Just 'return 1' looks okay to me.
> >
> > And, with this change, sysfs_slab_remove() is called even if the
> > shutdown is failed.
> > It's better not to have side effects when failing.
>
> If someone calls __kmem_cache_shutdown, he may want to release
> resources used by the slab cache as much as possible. If we continue,
> we may release more pages. From this point, is it an improvement?

My opinion is not strong but I still think that it's not useful enough
to complicate
the code.

If shutdown is failed, it implies there are some bugs and someone should fi=
x it.
Releasing more resources would mitigate the resource problem but doesn't
change the situation that someone should fix it soon.

Anyway, I don't object more if you don't agree with my opinion. In that cas=
e,
please fix not to call sysfs_slab_remove() when ret is 1.

Thanks.