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

[Shakeel Butt]

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.