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Date: Thu, 29 Jan 2026 16:47:52 -0800
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From: Shakeel Butt <shakeel.butt@linux.dev>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, 
	Johannes Weiner <hannes@cmpxchg.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_HI8JM9mZCr4-@linux.dev>
References: <20260129184054.910897-1-shakeel.butt@linux.dev>
 <aXvjdArhPpUNF8BI@casper.infradead.org>
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On Thu, Jan 29, 2026 at 10:47:16PM +0000, Matthew Wilcox wrote:
> 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?
> 

b8eddff8886b is about different stats NR_SHMEM_THPS & NR_FILE_THPS.
However as Johannes responded this code was broken even before memcg
awareness for NR_FILE_PAGES and NR_SHMEM.

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