xfs: improve metadata I/O merging in the elevator

Change all async metadata buffers to use [READ|WRITE]_META I/O types
so that the I/O doesn't get issued immediately. This allows merging of
adjacent metadata requests but still prioritises them over bulk data.
This shows a 10-15% improvement in sequential create speed of small
files.

Don't include the log buffers in this classification - leave them as
sync types so they are issued immediately.

Signed-off-by: Dave Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b23a7018eb90..cf7fc8a7fe6a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -152,6 +152,7 @@ struct inodes_stat_t {
 #define WRITE_SYNC_PLUG (WRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
 #define WRITE_SYNC      (WRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
 #define WRITE_ODIRECT_PLUG      (WRITE | (1 << BIO_RW_SYNCIO))
+#define WRITE_META      (WRITE | (1 << BIO_RW_META))
 #define SWRITE_SYNC_PLUG        \
                         (SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
 #define SWRITE_SYNC     (SWRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))