linux-kernel - Re: [External] Re: [PATCH 3/3] mm/slub: Fix release all resources used by a slab cache

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Message-ID: <CAMZfGtVBtRK=rA2CGGnOuTvHyXffVm7vE7m37MAMSbW8fkzjfg@mail.gmail.com>
Date:   Mon, 15 Jun 2020 15:50:16 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Joonsoo Kim <js1304@...il.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH 3/3] mm/slub: Fix release all resources
 used by a slab cache

On Mon, Jun 15, 2020 at 3:25 PM Joonsoo Kim <js1304@...il.com> wrote:
>
> 2020년 6월 15일 (월) 오후 3:41, Muchun Song <songmuchun@...edance.com>님이 작성:
> >
> > On Mon, Jun 15, 2020 at 2:23 PM Joonsoo Kim <js1304@...il.com> wrote:
> > >
> > > 2020년 6월 14일 (일) 오후 9:39, Muchun Song <songmuchun@...edance.com>님이 작성:
> > > >
> > > > The function of __kmem_cache_shutdown() is that release all resources
> > > > used by the slab cache, while currently it stop release resources when
> > > > the preceding node is not empty.
> > > >
> > > > Signed-off-by: Muchun Song <songmuchun@...edance.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 = 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 = 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 fix it.

Yeah, I agree with you.

> 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 case,
> please fix not to call sysfs_slab_remove() when ret is 1.
>

Yeah, we should call sysfs_slab_remove only when ret is zero. Thanks very
much.

-- 
Yours,
Muchun