linux-kernel - Re: [PATCH v2] mm/slub: Simplify __kmem_cache

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Date:   Sun, 5 Jun 2022 15:04:44 +0800
From:   Xiongwei Song <sxwjean@...il.com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     Xiongwei Song <sxwjean@...com>, 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>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <songmuchun@...edance.com>,
        "linux-mm @ kvack . org" <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Xiongwei Song <xiongwei.song@...driver.com>
Subject: Re: [PATCH v2] mm/slub: Simplify __kmem_cache_alias()

On Sat, Jun 4, 2022 at 5:43 PM Hyeonggon Yoo <42.hyeyoo@...il.com> wrote:
>
> On Fri, Jun 03, 2022 at 10:35:55PM +0800, sxwjean@...com wrote:
> > From: Xiongwei Song <xiongwei.song@...driver.com>
> >
> > There is no need to do anything if sysfs_slab_alias() return nonzero
> > value after getting a mergeable cache.
> >
> > Signed-off-by: Xiongwei Song <xiongwei.song@...driver.com>
> > Reviewed-by: Muchun Song <songmuchun@...edance.com>
> > ---
> > v2: Collect Reviewed-by tag from Muchun.
> > ---
> >  mm/slub.c | 8 +++-----
> >  1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index d8d5abf49f5f..9444277d669a 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -4861,6 +4861,9 @@ __kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
> >
> >       s = find_mergeable(size, align, flags, name, ctor);
> >       if (s) {
> > +             if (sysfs_slab_alias(s, name))
> > +                     return NULL;
> > +
> >               s->refcount++;
> >
>
> I think we should not expose sysfs attributes before initializing
> what can be read via sysfs attribute (object_size).
>
> >               /*
> > @@ -4869,11 +4872,6 @@ __kmem_cache_alias(const char *name, unsigned int size, unsigned int align,
> >                */
> >               s->object_size = max(s->object_size, size);
>
> this calculation should be done before sysfs_slab_alias().

Yeah, understood. Should we restore s->object_size and s->inuse if
sysfs_slab_alias() returns non zero value?

Regards,
Xiongwwei

>
> Thanks,
> Hyeonggon
>
> >               s->inuse = max(s->inuse, ALIGN(size, sizeof(void *)));
> > -
> > -             if (sysfs_slab_alias(s, name)) {
> > -                     s->refcount--;
> > -                     s = NULL;
> > -             }
> >       }
> >
> >       return s;
> > --
> > 2.30.2
> >
>