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

[Shakeel Butt <shakeel.butt@linux.dev>]

On Thu, Jan 29, 2026 at 07:32:14PM -0500, Johannes Weiner wrote:
> On Thu, Jan 29, 2026 at 10:40:54AM -0800, Shakeel Butt wrote:
> > @@ -2200,8 +2200,8 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
> >  	else
> >  		lruvec_stat_mod_folio(new_folio, NR_FILE_THPS, HPAGE_PMD_NR);
> >  
> > +	lruvec_stat_mod_folio(new_folio, NR_FILE_PAGES, HPAGE_PMD_NR);
> 
> The memcg breakage is more visible, but I think this has been broken
> for NUMA stats even longer. new_folio could also come from a different
> node than the subpages, after all.

Indeed you are right, so I should blame Kiryl instead of Song :P

> 
> >  	if (nr_none) {
> > -		lruvec_stat_mod_folio(new_folio, NR_FILE_PAGES, nr_none);
> >  		/* nr_none is always 0 for non-shmem. */
> >  		lruvec_stat_mod_folio(new_folio, NR_SHMEM, nr_none);
> 
> So AFAICT NR_SHMEM needs the same treatment.
> 
> It looks like that's been broken since f3f0e1d2150b ("khugepaged: add
> support of collapse for tmpfs/shmem pages").

Thanks, I will send v2 with correct handling of NR_SHMEM as well.