+ mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete.patch added to mm-unstable branch

+ mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/page_io: fix PSWPIN undercount for large folios in sio_read_complete()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: David Carlier <devnexen@gmail.com>
Subject: mm/page_io: fix PSWPIN undercount for large folios in sio_read_complete()
Date: Mon, 23 Mar 2026 23:13:15 +0000

sio_read_complete() uses sio->pages to account global PSWPIN vm events,
but sio->pages tracks the number of bvec entries (folios), not base pages.
For large folios this undercounts compared to the per-memcg path which
correctly uses folio_nr_pages(), and compared to the bdev read paths which
also use folio_nr_pages().

Use sio->len >> PAGE_SHIFT instead, which gives the correct base page
count since sio->len is accumulated via folio_size(folio).

Link: https://lkml.kernel.org/r/20260323231315.240137-1-devnexen@gmail.com
Fixes: a1a0dfd56f97 ("mm: handle THP in swap_*page_fs()")
Signed-off-by: David Carlier <devnexen@gmail.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page_io.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page_io.c~mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete
+++ a/mm/page_io.c
@@ -497,7 +497,7 @@ static void sio_read_complete(struct kio
 			folio_mark_uptodate(folio);
 			folio_unlock(folio);
 		}
-		count_vm_events(PSWPIN, sio->pages);
+		count_vm_events(PSWPIN, sio->len >> PAGE_SHIFT);
 	} else {
 		for (p = 0; p < sio->pages; p++) {
 			struct folio *folio = page_folio(sio->bvec[p].bv_page);
_

Patches currently in -mm which might be from devnexen@gmail.com are

mm-hugetlb-restore-reservation-on-error-in-hugetlb_mfill_atomic_pte-resubmission-path.patch
mm-page_io-fix-pswpin-undercount-for-large-folios-in-sio_read_complete.patch