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, 30 insertions, 28 deletions

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 277966a..c8e20b6 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -199,12 +199,17 @@ struct page *find_data_page(struct inode *inode, pgoff_t index)
 	if (!page)
 		return ERR_PTR(-ENOMEM);
 
+	if (PageUptodate(page)) {
+		unlock_page(page);
+		return page;
+	}
+
 	err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-	if (err) {
-		f2fs_put_page(page, 1);
-		return ERR_PTR(err);
+	wait_on_page_locked(page);
+	if (!PageUptodate(page)) {
+		f2fs_put_page(page, 0);
+		return ERR_PTR(-EIO);
 	}
-	unlock_page(page);
 	return page;
 }
 
@@ -241,9 +246,13 @@ struct page *get_lock_data_page(struct inode *inode, pgoff_t index)
 	BUG_ON(dn.data_blkaddr == NULL_ADDR);
 
 	err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-	if (err) {
-		f2fs_put_page(page, 1);
+	if (err)
 		return ERR_PTR(err);
+
+	lock_page(page);
+	if (!PageUptodate(page)) {
+		f2fs_put_page(page, 1);
+		return ERR_PTR(-EIO);
 	}
 	return page;
 }
@@ -283,14 +292,17 @@ struct page *get_new_data_page(struct inode *inode, pgoff_t index,
 
 	if (dn.data_blkaddr == NEW_ADDR) {
 		zero_user_segment(page, 0, PAGE_CACHE_SIZE);
+		SetPageUptodate(page);
 	} else {
 		err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-		if (err) {
-			f2fs_put_page(page, 1);
+		if (err)
 			return ERR_PTR(err);
+		lock_page(page);
+		if (!PageUptodate(page)) {
+			f2fs_put_page(page, 1);
+			return ERR_PTR(-EIO);
 		}
 	}
-	SetPageUptodate(page);
 
 	if (new_i_size &&
 		i_size_read(inode) < ((index + 1) << PAGE_CACHE_SHIFT)) {
@@ -325,22 +337,14 @@ static void read_end_io(struct bio *bio, int err)
 
 /*
  * Fill the locked page with data located in the block address.
- * Read operation is synchronous, and caller must unlock the page.
+ * Return unlocked page.
  */
 int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 					block_t blk_addr, int type)
 {
 	struct block_device *bdev = sbi->sb->s_bdev;
-	bool sync = (type == READ_SYNC);
 	struct bio *bio;
 
-	/* This page can be already read by other threads */
-	if (PageUptodate(page)) {
-		if (!sync)
-			unlock_page(page);
-		return 0;
-	}
-
 	down_read(&sbi->bio_sem);
 
 	/* Allocate a new bio */
@@ -354,18 +358,12 @@ int f2fs_readpage(struct f2fs_sb_info *sbi, struct page *page,
 		kfree(bio->bi_private);
 		bio_put(bio);
 		up_read(&sbi->bio_sem);
+		f2fs_put_page(page, 1);
 		return -EFAULT;
 	}
 
 	submit_bio(type, bio);
 	up_read(&sbi->bio_sem);
-
-	/* wait for read completion if sync */
-	if (sync) {
-		lock_page(page);
-		if (PageError(page))
-			return -EIO;
-	}
 	return 0;
 }
 
@@ -636,18 +634,22 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 
 		/* Reading beyond i_size is simple: memset to zero */
 		zero_user_segments(page, 0, start, end, PAGE_CACHE_SIZE);
-		return 0;
+		goto out;
 	}
 
 	if (dn.data_blkaddr == NEW_ADDR) {
 		zero_user_segment(page, 0, PAGE_CACHE_SIZE);
 	} else {
 		err = f2fs_readpage(sbi, page, dn.data_blkaddr, READ_SYNC);
-		if (err) {
-			f2fs_put_page(page, 1);
+		if (err)
 			return err;
+		lock_page(page);
+		if (!PageUptodate(page)) {
+			f2fs_put_page(page, 1);
+			return -EIO;
 		}
 	}
+out:
 	SetPageUptodate(page);
 	clear_cold_data(page);
 	return 0;