Re: [PATCH RFC 05/12] mm/slab: abstract slabobj_ext.objcg access

[Omar Sandoval <osandov@osandov.com>]

On Fri, Jul 17, 2026 at 12:00:29PM +0200, Vlastimil Babka (SUSE) wrote:
> On 7/15/26 12:10, Vlastimil Babka (SUSE) wrote:
> > In preparation for changes to the structure, abstract access to the
> > objcg field with a slab_obj_ext_objcgp() function.
> > Rename the field to _objcg to make an unexpected direct access a compile
> > error.
> > 
> > No functional change intended.
> > 
> > Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> 
> Hm sashiko finds [1] that this is breaks tools/mm/show_page_info.py
> 
> But I think it was already buggy. get_memcg_info() is supposed to return
> memcg info for a page but in case of MEMCG_DATA_OBJEXTS there's no such info
> for the whole page, there is only for individual slab objects and it doesn't
> know which object so it effectively gets the first one. I think it should
> just stop handling MEMCG_DATA_OBJEXTS, but that's a fix that should be sent
> unrelated to this series.
> 
> There's also tools/cgroup/memcg_slabinfo.py and that I think has been
> already broken with memalloc profiling as it assuems slab.memcg_data is
> still a raw struct obj_cgroup * and not struct slabobj_ext.
> 
> I think it will be easier to fix it at once to handle the layout after this
> series than trying to fix it first to handle the pre-series layout and then
> update it with every relevant change.
> 
> [1]
> https://sashiko.dev/#/patchset/20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org?part=5

FWIW, if these scripts were in the drgn repo with test cases, these
breakages would be caught by our CI and someone (usually me) would fix
them up promptly :)