Commit 9e0d0ddf authored Mar 20, 2026 by Alexandre Ghiti Committed by Andrew Morton Mar 27, 2026

mm/swap: fix swap cache memcg accounting

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.

Link: https://lkml.kernel.org/r/20260320050601.1833108-1-alex@ghiti.fr


Fixes: 2732acda ("mm, swap: use swap cache as the swap in synchronize layer")
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Acked-by: Kairui Song <kasong@tencent.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 26d3dca2

mm/swap_state.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -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);