Re: [PATCH v2] mm/slub: Simplify __kmem_cache_alias()

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

On Sun, Jun 05, 2022 at 03:04:44PM +0800, Xiongwei Song wrote:
> On Sat, Jun 4, 2022 at 5:43 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
> >
> > On Fri, Jun 03, 2022 at 10:35:55PM +0800, sxwjean@me.com wrote:
> > > From: Xiongwei Song <xiongwei.song@windriver.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@windriver.com>
> > > Reviewed-by: Muchun Song <songmuchun@bytedance.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().
> 

Sorry for the late reply.

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

In my opinion, yes.

Thanks,
Hyeonggon

> 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
> > >
> >

-- 
Thanks,
Hyeonggon