[PATCH] btrfs: add block plug for .writepages

[Namjae Jeon <linkinjeon@gmail.com>]

Add block plug for btrfs .writepages. Block plug is helpful to reduce block lock contention.

Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
---
 fs/btrfs/extent_io.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index d418164..8f2d6bd 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2388,6 +2388,7 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
 	pgoff_t end;		/* Inclusive */
 	int scanned = 0;
 	int tag;
+	struct blk_plug plug;
 
 	pagevec_init(&pvec, 0);
 	if (wbc->range_cyclic) {
@@ -2405,6 +2406,8 @@ static int extent_write_cache_pages(struct extent_io_tree *tree,
 retry:
 	if (wbc->sync_mode == WB_SYNC_ALL)
 		tag_pages_for_writeback(mapping, index, end);
+
+	blk_start_plug(&plug);
 	while (!done && !nr_to_write_done && (index <= end) &&
 	       (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag,
 			min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
@@ -2468,6 +2471,7 @@ retry:
 		pagevec_release(&pvec);
 		cond_resched();
 	}
+	blk_finish_plug(&plug);
 	if (!scanned && !done) {
 		/*
 		 * We hit the last page and there is more work to be done: wrap
-- 
1.7.4.4