Re: slab warning: kmem_cache of name 'dm_bufio_buffer' already exists

[Pedro Falcato <pedro.falcato@gmail.com>]

On Fri, Nov 8, 2024 at 9:56 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 11/6/24 22:22, Mikulas Patocka wrote:
> >
> >
> > On Wed, 6 Nov 2024, Vlastimil Babka wrote:
> >
> >> On 11/6/24 13:05, Mikulas Patocka wrote:
> >> >
> >> >
> >> > On Wed, 6 Nov 2024, Vlastimil Babka wrote:
> >> >
> >> >> On 11/6/24 12:19, Mikulas Patocka wrote:
> >> >> > Hi
> >> >>
> >> >> Hi,
> >> >>
> >> >> > The commit 4c39529663b93165953ecf9b1a9ea817358dcd06 ("slab: Warn on
> >> >> > duplicate cache names when DEBUG_VM=y") is causing large number of
> >> >> > warnings about "dm_bufio_buffer", "dm_bufio_buffer-%u" (and other) device
> >> >> > mapper caches.
> >> >>
> >> >> Hmm wonder why nobody run into this before. We thought the code that would
> >> >> cause the warning would be all fixed before introducing it, but we missed
> >> >> some, sorry.
> >> >>
> >> >> > I'd like to ask - how to properly fix it?
> >> >> >
> >> >> > We create a "dm_bufio_buffer" or "dm_bufio_buffer-%u" cache with every dm
> >> >> > bufio client. It used to work (and the duplicate caches are merged), but
> >> >>
> >> >> Note the merging can be disabled so then it's really several caches with
> >> >> exactly same name in /proc/slabinfo and inability to create their
> >> >> sysfs/debugfs directories.
> >> >
> >> > Would it be sensible to allow merging caches with the same name and same
> >> > attributes and only warn if there are caches with the same name and
> >> > different attributes?
> >>
> >> We might consider that.
> >
> > That would be good - so that users don't have to write their own slab
> > cache merge logic.
>
> So Pedro, wanna do that? Or Hyeonggon maybe? :)
>

I'll take a look this weekend, now that our polish friend passed me
the smoking gun ;)

-- 
Pedro