Re: [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in collapse_file()

[Shakeel Butt]

On Thu, Jan 29, 2026 at 10:50:15AM -0800, Andrew Morton wrote:
> On Thu, 29 Jan 2026 10:40:54 -0800 Shakeel Butt <shakeel.butt@xxxxxxxxx> wrote:
> 
> > In META's fleet, we are seeing high level cgroups with zero file memcg
> > stat but their descendants have non-zero file stat. This should not be
> > possible. On further inspection by looking at kernel data structures
> > though drgn, it was revealed that the high level cgroups have negative
> > file stat which was aggregated from their children.
> > 
> > Another interesting point was that this specific issue start happening
> > more often as we started deploying thp-always more widely which
> > indicates some correlation between file memory and THPs and indeed it
> > was found that file memcg stat accounting is buggy in the collapse code
> > path from the start.
> 
> So this has no known runtime effect apart from incorrect accounting?

Yes just an accounting bug.

> 
> > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> 
> Should we cc:stable?

I think so.