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

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Message-ID: <3b05b046-9d0e-c9a4-5d3d-62b815ca020d@linux.alibaba.com>
Date:   Wed, 21 Jun 2023 14:46:44 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Jan Glauber <jglauber@...italocean.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Huang, Ying" <ying.huang@...el.com>
Subject: Re: [PATCH v2] mm: Fix shmem THP counters on migration


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@...italocean.com>
> ---

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
>