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

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Message-ID: <aXvjdArhPpUNF8BI@casper.infradead.org>
Date: Thu, 29 Jan 2026 22:47:16 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.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:
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")

Are you sure this is the right Fixes?  99cb0dbd47a1 wasn't cgroup
aware:

        if (nr_none) {
                struct zone *zone = page_zone(new_page);

                __mod_node_page_state(zone->zone_pgdat, NR_FILE_PAGES, nr_none);
-               __mod_node_page_state(zone->zone_pgdat, NR_SHMEM, nr_none);
+               if (is_shmem)
+                       __mod_node_page_state(zone->zone_pgdat,
+                                             NR_SHMEM, nr_none);
        }

b8eddff8886b added cgroup support:

        if (is_shmem)
-               __inc_node_page_state(new_page, NR_SHMEM_THPS);
+               __inc_lruvec_page_state(new_page, NR_SHMEM_THPS);
        else {
-               __inc_node_page_state(new_page, NR_FILE_THPS);
+               __inc_lruvec_page_state(new_page, NR_FILE_THPS);
                filemap_nr_thps_inc(mapping);
        }

which would seem like the right Fixes: to me?

> Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
> ---
>  mm/khugepaged.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 1d994b6c58c6..1cf8e154e214 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -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);
>  	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);
>  	}
> @@ -2238,6 +2238,8 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
>  	 */
>  	list_for_each_entry_safe(folio, tmp, &pagelist, lru) {
>  		list_del(&folio->lru);
> +		lruvec_stat_mod_folio(folio, NR_FILE_PAGES,
> +				      -folio_nr_pages(folio));
>  		folio->mapping = NULL;
>  		folio_clear_active(folio);
>  		folio_clear_unevictable(folio);
> -- 
> 2.47.3
> 
>