* Re: [PATCH] mm/swap: fix swap cache memcg accounting
2026-03-20 5:05 [PATCH] mm/swap: fix swap cache memcg accounting Alexandre Ghiti
@ 2026-03-20 6:57 ` Kairui Song
2026-03-20 14:24 ` Johannes Weiner
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Kairui Song @ 2026-03-20 6:57 UTC (permalink / raw)
To: Alexandre Ghiti
Cc: Andrew Morton, Chris Li, Kairui Song, Kemeng Shi, Nhat Pham,
Baoquan He, Barry Song, hannes, kernel-team, linux-mm,
linux-kernel
On Fri, Mar 20, 2026 at 06:05:59AM +0800, Alexandre Ghiti wrote:
> The swap readahead path was recently refactored and while doing this,
> the order between the charging of the folio in the memcg and the addition
> of the folio in the swap cache was inverted.
>
> Since the accounting of the folio is done while adding the folio to the
> swap cache and the folio is not charged in the memcg yet, the accounting
> is then done at the node level, which is wrong.
>
> Fix this by charging the folio in the memcg before adding it to the swap cache.
>
> Fixes: 2732acda82c9 ("mm, swap: use swap cache as the swap in synchronize layer")
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
> mm/swap_state.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 6d0eef7470be..48aff2c917c0 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -494,6 +494,10 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
>
> __folio_set_locked(folio);
> __folio_set_swapbacked(folio);
> +
> + if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry))
> + goto failed;
> +
Thanks! I was worrying charging it first could cause thrashing, raced
swapin will cause multiple charge and failed one will uncharge, so
I put the charge after insert into cache, completely forgot about
the lruvec static info part.
For a quick fix this this is clean and good enough, and it
doesn't effect the most performance sensitive part, mTHP and
ZRAM would have `charged == true` here so they are not effected.
Later we can move the lruvec static info out of
__swap_cache_add_folio after the charge, maybe I'll do this with
someother follow up optimzation together, then everything should
be perfect.
And I think we need Cc stable here.
Acked-by: Kairui Song <kasong@tencent.com>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm/swap: fix swap cache memcg accounting
2026-03-20 5:05 [PATCH] mm/swap: fix swap cache memcg accounting Alexandre Ghiti
2026-03-20 6:57 ` Kairui Song
@ 2026-03-20 14:24 ` Johannes Weiner
2026-03-20 19:31 ` Nhat Pham
2026-03-21 8:08 ` Chris Li
3 siblings, 0 replies; 5+ messages in thread
From: Johannes Weiner @ 2026-03-20 14:24 UTC (permalink / raw)
To: Alexandre Ghiti
Cc: Andrew Morton, Chris Li, Kairui Song, Kemeng Shi, Nhat Pham,
Baoquan He, Barry Song, kernel-team, linux-mm, linux-kernel
On Fri, Mar 20, 2026 at 06:05:59AM +0100, Alexandre Ghiti wrote:
> The swap readahead path was recently refactored and while doing this,
> the order between the charging of the folio in the memcg and the addition
> of the folio in the swap cache was inverted.
>
> Since the accounting of the folio is done while adding the folio to the
> swap cache and the folio is not charged in the memcg yet, the accounting
> is then done at the node level, which is wrong.
>
> Fix this by charging the folio in the memcg before adding it to the swap cache.
>
> Fixes: 2732acda82c9 ("mm, swap: use swap cache as the swap in synchronize layer")
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm/swap: fix swap cache memcg accounting
2026-03-20 5:05 [PATCH] mm/swap: fix swap cache memcg accounting Alexandre Ghiti
2026-03-20 6:57 ` Kairui Song
2026-03-20 14:24 ` Johannes Weiner
@ 2026-03-20 19:31 ` Nhat Pham
2026-03-21 8:08 ` Chris Li
3 siblings, 0 replies; 5+ messages in thread
From: Nhat Pham @ 2026-03-20 19:31 UTC (permalink / raw)
To: Alexandre Ghiti
Cc: Andrew Morton, Chris Li, Kairui Song, Kemeng Shi, Baoquan He,
Barry Song, hannes, kernel-team, linux-mm, linux-kernel
On Thu, Mar 19, 2026 at 10:06 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> The swap readahead path was recently refactored and while doing this,
> the order between the charging of the folio in the memcg and the addition
> of the folio in the swap cache was inverted.
>
> Since the accounting of the folio is done while adding the folio to the
> swap cache and the folio is not charged in the memcg yet, the accounting
> is then done at the node level, which is wrong.
>
> Fix this by charging the folio in the memcg before adding it to the swap cache.
>
> Fixes: 2732acda82c9 ("mm, swap: use swap cache as the swap in synchronize layer")
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
> mm/swap_state.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 6d0eef7470be..48aff2c917c0 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -494,6 +494,10 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
>
> __folio_set_locked(folio);
> __folio_set_swapbacked(folio);
> +
> + if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry))
> + goto failed;
> +
> for (;;) {
> ret = swap_cache_add_folio(folio, entry, &shadow);
> if (!ret)
> @@ -514,11 +518,6 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
> goto failed;
> }
>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] mm/swap: fix swap cache memcg accounting
2026-03-20 5:05 [PATCH] mm/swap: fix swap cache memcg accounting Alexandre Ghiti
` (2 preceding siblings ...)
2026-03-20 19:31 ` Nhat Pham
@ 2026-03-21 8:08 ` Chris Li
3 siblings, 0 replies; 5+ messages in thread
From: Chris Li @ 2026-03-21 8:08 UTC (permalink / raw)
To: Alexandre Ghiti
Cc: Andrew Morton, Kairui Song, Kemeng Shi, Nhat Pham, Baoquan He,
Barry Song, hannes, kernel-team, linux-mm, linux-kernel
On Thu, Mar 19, 2026 at 10:06 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> The swap readahead path was recently refactored and while doing this,
> the order between the charging of the folio in the memcg and the addition
> of the folio in the swap cache was inverted.
>
> Since the accounting of the folio is done while adding the folio to the
> swap cache and the folio is not charged in the memcg yet, the accounting
> is then done at the node level, which is wrong.
>
> Fix this by charging the folio in the memcg before adding it to the swap cache.
>
> Fixes: 2732acda82c9 ("mm, swap: use swap cache as the swap in synchronize layer")
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Chris Li <chrisl@kernel.org>
Chris
> ---
> mm/swap_state.c | 9 ++++-----
> 1 file changed, 4 insertions(+), 5 deletions(-)
>
> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 6d0eef7470be..48aff2c917c0 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -494,6 +494,10 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
>
> __folio_set_locked(folio);
> __folio_set_swapbacked(folio);
> +
> + if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry))
> + goto failed;
> +
> for (;;) {
> ret = swap_cache_add_folio(folio, entry, &shadow);
> if (!ret)
> @@ -514,11 +518,6 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
> goto failed;
> }
>
> - if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry)) {
> - swap_cache_del_folio(folio);
> - goto failed;
> - }
> -
> memcg1_swapin(entry, folio_nr_pages(folio));
> if (shadow)
> workingset_refault(folio, shadow);
> --
> 2.53.0
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread