[PATCH] block_write_full_page: switch synchronous writes to use WRITE_SYNC_PLUG

Theodore Tso
2009-04-07T22:19:54Z

Now that we have a distinction between WRITE_SYNC and WRITE_SYNC_PLUG,
use WRITE_SYNC_PLUG in __block_write_full_page() to avoid unplugging
the block device I/O queue between each page that gets flushed out.

The upstream callers of block_write_full_page() which wait for the
writes to finish call wait_on_buffer(), wait_on_writeback_range()
(which ultimately calls sync_page(), which calls
blk_run_backing_dev(), which will unplug the device queue), and so on.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---

We should get this applied to avoid any performance regressions
resulting from commit a64c8610.

fs/buffer.c | 3 ++-
1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 977e12a..95b5390 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1646,7 +1646,8 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
struct buffer_head *bh, *head;
const unsigned blocksize = 1 << inode->i_blkbits;
int nr_underway = 0;
- int write_op = (wbc->sync_mode == WB_SYNC_ALL ? WRITE_SYNC : WRITE);
+ int write_op = (wbc->sync_mode == WB_SYNC_ALL ?
+ WRITE_SYNC_PLUG : WRITE);

BUG_ON(!PageLocked(page));

--
1.5.6.3