[PATCH v2] f2fs: add a fast path in finish_preallocate_blocks()

[Chao Yu <chao@kernel.org>]

This patch uses i_sem to protect access/update on f2fs_inode_info.flag
in finish_preallocate_blocks(), it avoids grabbing inode_lock() in
each open().

Signed-off-by: Chao Yu <chao@kernel.org>
---
v2:
- get rid of read lock during querying FI_OPENED_FILE once we held
inode lock.
 fs/f2fs/file.c | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index abbcbb5865a3..a71946976761 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -554,19 +554,21 @@ static int f2fs_file_mmap(struct file *file, struct vm_area_struct *vma)
 
 static int finish_preallocate_blocks(struct inode *inode)
 {
-	int ret;
+	int ret = 0;
+	bool opened;
 
-	inode_lock(inode);
-	if (is_inode_flag_set(inode, FI_OPENED_FILE)) {
-		inode_unlock(inode);
+	f2fs_down_read(&F2FS_I(inode)->i_sem);
+	opened = is_inode_flag_set(inode, FI_OPENED_FILE);
+	f2fs_up_read(&F2FS_I(inode)->i_sem);
+	if (opened)
 		return 0;
-	}
 
-	if (!file_should_truncate(inode)) {
-		set_inode_flag(inode, FI_OPENED_FILE);
-		inode_unlock(inode);
-		return 0;
-	}
+	inode_lock(inode);
+	if (is_inode_flag_set(inode, FI_OPENED_FILE))
+		goto out_unlock;
+
+	if (!file_should_truncate(inode))
+		goto out_update;
 
 	f2fs_down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
 	filemap_invalidate_lock(inode->i_mapping);
@@ -576,16 +578,17 @@ static int finish_preallocate_blocks(struct inode *inode)
 
 	filemap_invalidate_unlock(inode->i_mapping);
 	f2fs_up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
-
-	if (!ret)
-		set_inode_flag(inode, FI_OPENED_FILE);
-
-	inode_unlock(inode);
 	if (ret)
-		return ret;
+		goto out_unlock;
 
 	file_dont_truncate(inode);
-	return 0;
+out_update:
+	f2fs_down_write(&F2FS_I(inode)->i_sem);
+	set_inode_flag(inode, FI_OPENED_FILE);
+	f2fs_up_write(&F2FS_I(inode)->i_sem);
+out_unlock:
+	inode_unlock(inode);
+	return ret;
 }
 
 static int f2fs_file_open(struct inode *inode, struct file *filp)
-- 
2.48.1