Re: [PATCH v2] mm: Fix shmem THP counters on migration

[Baolin Wang]

Cc: Huang Ying

On 6/19/2023 6:33 PM, Jan Glauber wrote:
> The per node numa_stat values for shmem don't change on
> page migration for THP:
>
>    grep shmem /sys/fs/cgroup/machine.slice/.../memory.numa_stat:
>
>      shmem N0=1092616192 N1=10485760
>      shmem_thp N0=1092616192 N1=10485760
>
>    migratepages 9181 0 1:
>
>      shmem N0=0 N1=1103101952
>      shmem_thp N0=1092616192 N1=10485760
>
> Fix that by updating shmem_thp counters likewise to shmem counters
> on page migration.
>
> Signed-off-by: Jan Glauber <jglauber@xxxxxxxxxxxxxxxx>
> ---

Please add your change history.

>   mm/migrate.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 01cac26a3127..d2ba786ea105 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -492,6 +492,11 @@ int folio_migrate_mapping(struct address_space *mapping,
>   		if (folio_test_swapbacked(folio) && !folio_test_swapcache(folio)) {
>   			__mod_lruvec_state(old_lruvec, NR_SHMEM, -nr);
>   			__mod_lruvec_state(new_lruvec, NR_SHMEM, nr);
> +
> +			if (folio_test_transhuge(folio)) {

I am afraid this validation is fragile, IIUC the file backed folio can 
contain various numbers of pages in future.

So seems using folio_test_pmd_mappable() seems more suitable for THP.

> +				__mod_lruvec_state(old_lruvec, NR_SHMEM_THPS, -nr);
> +				__mod_lruvec_state(new_lruvec, NR_SHMEM_THPS, nr);
> +			}
>   		}
>   #ifdef CONFIG_SWAP
>   		if (folio_test_swapcache(folio)) {
> --
> 2.25.1