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Date: Thu, 29 Jan 2026 16:50:57 -0800
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From: Shakeel Butt <shakeel.butt@linux.dev>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, 
	Rik van Riel <riel@surriel.com>, Song Liu <songliubraving@fb.com>, 
	Kiryl Shutsemau <kas@kernel.org>, Usama Arif <usamaarif642@gmail.com>, 
	David Hildenbrand <david@kernel.org>, Lorenzo Stoakes <lorenzo.stoakes@oracle.com>, 
	Zi Yan <ziy@nvidia.com>, Baolin Wang <baolin.wang@linux.alibaba.com>, 
	"Liam R . Howlett" <Liam.Howlett@oracle.com>, Nico Pache <npache@redhat.com>, 
	Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>, Barry Song <baohua@kernel.org>, 
	Lance Yang <lance.yang@linux.dev>, Meta kernel team <kernel-team@meta.com>, linux-mm@kvack.org, 
	cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in
 collapse_file()
Message-ID: <aXv_5Gl6L-1eXYQd@linux.dev>
References: <20260129184054.910897-1-shakeel.butt@linux.dev>
 <aXv8DjjJ3zqZEsgQ@cmpxchg.org>
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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.