linux-kernel - [PATCH v4 9/9] mm/shmem, swap: fix major fault counting

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Message-ID: <20250704181748.63181-10-ryncsn@gmail.com>
Date: Sat,  5 Jul 2025 02:17:48 +0800
From: Kairui Song <ryncsn@...il.com>
To: linux-mm@...ck.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Matthew Wilcox <willy@...radead.org>,
	Kemeng Shi <shikemeng@...weicloud.com>,
	Chris Li <chrisl@...nel.org>,
	Nhat Pham <nphamcs@...il.com>,
	Baoquan He <bhe@...hat.com>,
	Barry Song <baohua@...nel.org>,
	linux-kernel@...r.kernel.org,
	Kairui Song <kasong@...cent.com>
Subject: [PATCH v4 9/9] mm/shmem, swap: fix major fault counting

From: Kairui Song <kasong@...cent.com>

If the swapin failed, don't update the major fault count. There is a
long existing comment for doing it this way, now with previous cleanups,
we can finally fix it.

Signed-off-by: Kairui Song <kasong@...cent.com>
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
---
 mm/shmem.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 646b1db9501c..b03b5bf2df38 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2321,12 +2321,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 	/* Look it up and read it in.. */
 	folio = swap_cache_get_folio(swap, NULL, 0);
 	if (!folio) {
-		/* Or update major stats only when swapin succeeds?? */
-		if (fault_type) {
-			*fault_type |= VM_FAULT_MAJOR;
-			count_vm_event(PGMAJFAULT);
-			count_memcg_event_mm(fault_mm, PGMAJFAULT);
-		}
 		if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) {
 			/* Direct mTHP swapin skipping swap cache & readhaed */
 			folio = shmem_swapin_direct(inode, vma, index, swap,
@@ -2346,6 +2340,11 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 				goto failed;
 			}
 		}
+		if (fault_type) {
+			*fault_type |= VM_FAULT_MAJOR;
+			count_vm_event(PGMAJFAULT);
+			count_memcg_event_mm(fault_mm, PGMAJFAULT);
+		}
 	}
 
 	if (order > folio_order(folio)) {
-- 
2.50.0