f2fs: reduce unncessary locking pages during read

This patch reduces redundant locking and unlocking pages during read operations.
In f2fs_readpage, let's use wait_on_page_locked() instead of lock_page.
And then, when we need to modify any data finally, let's lock the page so that
we can avoid lock contention.

[readpage rule]
- The f2fs_readpage returns unlocked page, or released page too in error cases.
- Its caller should handle read error, -EIO, after locking the page, which
  indicates read completion.
- Its caller should check PageUptodate after grab_cache_page.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Reviewed-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 2b6fc131e2ce..d947e66ee8a8 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -57,13 +57,15 @@ repeat:
                 cond_resched();
                 goto repeat;
         }
-        if (f2fs_readpage(sbi, page, index, READ_SYNC)) {
-                f2fs_put_page(page, 1);
+        if (PageUptodate(page))
+                goto out;
+
+        if (f2fs_readpage(sbi, page, index, READ_SYNC))
                 goto repeat;
-        }
-        mark_page_accessed(page);
 
-        /* We do not allow returning an errorneous page */
+        lock_page(page);
+out:
+        mark_page_accessed(page);
         return page;
 }