[PATCH] fs/buffer.c: Add checking buffer head stat before clear

[Shaokun Zhang]

From: Yang Guo <guoya...@huawei.com>

clear_buffer_new() is used to clear buffer new stat. When PAGE_SIZE
is 64K, most buffer heads in the list are not needed to clear.
clear_buffer_new() has an enpensive atomic modification operation,
Let's add checking buffer head before clear it as __block_write_begin_int
does which is good for performance.

Cc: Alexander Viro <v...@zeniv.linux.org.uk>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Nick Piggin <npig...@suse.de>
Signed-off-by: Yang Guo <guoya...@huawei.com>
Signed-off-by: Shaokun Zhang <zhangshao...@hisilicon.com>
---
 fs/buffer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 32647d2011df..f1c3a5b27a90 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2083,7 +2083,8 @@ static int __block_commit_write(struct inode *inode, 
struct page *page,
                        set_buffer_uptodate(bh);
                        mark_buffer_dirty(bh);
                }
-               clear_buffer_new(bh);
+               if (buffer_new(bh))
+                       clear_buffer_new(bh);
 
                block_start = block_end;
                bh = bh->b_this_page;
-- 
2.7.4