ext4: add block plug for .writepages

Add block plug for ext4 .writepages. Though ext4 .writepages
already handles request merge very well, block plug is still
helpful to reduce block lock contention.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 4863238c3754..081bb25a9ad3 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2160,6 +2160,7 @@ static int ext4_da_writepages(struct address_space *mapping,
         struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb);
         pgoff_t done_index = 0;
         pgoff_t end;
+        struct blk_plug plug;
 
         trace_ext4_da_writepages(inode, wbc);
 
@@ -2238,6 +2239,7 @@ retry:
         if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages)
                 tag_pages_for_writeback(mapping, index, end);
 
+        blk_start_plug(&plug);
         while (!ret && wbc->nr_to_write > 0) {
 
                 /*
@@ -2302,6 +2304,7 @@ retry:
                          */
                         break;
         }
+        blk_finish_plug(&plug);
         if (!io_done && !cycled) {
                 cycled = 1;
                 index = 0;