# \[PATCH 11/14\] mm: use SWP\_SYNCHRONOUS\_IO more intelligently

- From: Christoph Hellwig \<hch@lst.de\>
- Date: 2020-07-24 07:34:25 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2020/07/185078
- Thread: https://ratatoskr.run/linux-block/2020/07/185071/t.md

```text
There is no point in trying to call bdev_read_page if SWP_SYNCHRONOUS_IO
is not set, as the device won't support it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/page_io.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/mm/page_io.c b/mm/page_io.c
index ccda7679008851..7eef3c84766abc 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -403,15 +403,17 @@ int swap_readpage(struct page *page, bool synchronous)
 		goto out;
 	}
 
-	ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
-	if (!ret) {
-		if (trylock_page(page)) {
-			swap_slot_free_notify(page);
-			unlock_page(page);
-		}
+	if (sis->flags & SWP_SYNCHRONOUS_IO) {
+		ret = bdev_read_page(sis->bdev, swap_page_sector(page), page);
+		if (!ret) {
+			if (trylock_page(page)) {
+				swap_slot_free_notify(page);
+				unlock_page(page);
+			}
 
-		count_vm_event(PSWPIN);
-		goto out;
+			count_vm_event(PSWPIN);
+			goto out;
+		}
 	}
 
 	ret = 0;
-- 
2.27.0
```