linux-kernel - Re: [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in collapse

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aXv8DjjJ3zqZEsgQ@cmpxchg.org>
Date: Thu, 29 Jan 2026 19:32:14 -0500
From: Johannes Weiner <hannes@...xchg.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...riel.com>, Song Liu <songliubraving@...com>,
	Kiryl Shutsemau <kas@...nel.org>,
	Usama Arif <usamaarif642@...il.com>,
	David Hildenbrand <david@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R . Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Lance Yang <lance.yang@...ux.dev>,
	Meta kernel team <kernel-team@...a.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: khugepaged: fix NR_FILE_PAGES accounting in
 collapse_file()

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.

>  	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").

Anon pages avoided this, because their accounting is done in rmap.c
when the pmd is mapped and the ptes zapped.