From: David Carlier <devnexen@gmail.com>
Date: Thu, 2 Apr 2026 06:14:07 +0000 (+0100)
Subject: mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=df620ec4d4d703f11f3b0adecd4450c34489e0f1;p=thirdparty%2Fkernel%2Flinux.git

mm/page_io: use sio->len for PSWPIN accounting in sio_read_complete()

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.

While large folios cannot currently reach this path (SWP_FS_OPS and
SWP_SYNCHRONOUS_IO are mutually exclusive, and mTHP swap-in allocation is
gated on SWP_SYNCHRONOUS_IO), the accounting is semantically inconsistent
with the per-memcg path which correctly uses 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://lore.kernel.org/20260402061408.36119-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: NeilBrown <neil@brown.name>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/page_io.c b/mm/page_io.c
index 93d03d9e2a6a..70cea9e24d2f 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -497,7 +497,7 @@ static void sio_read_complete(struct kiocb *iocb, long ret)
 			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);