Re: [RFC] SL[AUO]B common code 8/9] slabs: list addition move to slab_common

Christoph Lameter
2012-05-16T14:33:45Z

On Wed, 16 May 2012, Glauber Costa wrote:

> > Index: linux-2.6/mm/slab_common.c
> > ===================================================================
> > --- linux-2.6.orig/mm/slab_common.c 2012-05-14 08:39:27.859145830 -0500
> > +++ linux-2.6/mm/slab_common.c 2012-05-14 08:39:29.827145790 -0500
> > @@ -98,6 +98,9 @@ struct kmem_cache *kmem_cache_create(con
> >
> > s = __kmem_cache_create(name, size, align, flags, ctor);
> >
> > + if (s&& s->refcount == 1)
> > + list_add(&s->list,&slab_caches);
> > +
> > oops:
>
> I personally think that the refcount == 1 test is too fragile.
> It happens to be true, and is likely to be true in the future, but there is no
> particular reason that is *has* to be true forever.

Its not fragile since a refcount will always be one for a slab that was
just created. There is no possible other reference to it since the
subsystem using it has never received a pointer to the kmem_cache struct
yet.

> Also, the only reasons it exists, seems to be to go around the fact that the
> slab already adds the kmalloc caches to a list in a slightly different way.
> And there has to be cleaner ways to achieve that.

The reason it exists is to distinguish the case of an alias creation from
a true kmem_cache instatiation. The alias does not need to be added to the
list of slabs.