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

[Vlastimil Babka <vbabka@suse.cz>]

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? :)