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>

fs/xfs/linux-2.6/xfs_buf.c

@@ -1149,10 +1149,14 @@ _xfs_buf_ioapply(
 	if (bp->b_flags & XBF_ORDERED) {
 		ASSERT(!(bp->b_flags & XBF_READ));
 		rw = WRITE_BARRIER;
-	} else if (bp->b_flags & _XBF_RUN_QUEUES) {
+	} else if (bp->b_flags & XBF_LOG_BUFFER) {
 		ASSERT(!(bp->b_flags & XBF_READ_AHEAD));
 		bp->b_flags &= ~_XBF_RUN_QUEUES;
 		rw = (bp->b_flags & XBF_WRITE) ? WRITE_SYNC : READ_SYNC;
+	} else if (bp->b_flags & _XBF_RUN_QUEUES) {
+		ASSERT(!(bp->b_flags & XBF_READ_AHEAD));
+		bp->b_flags &= ~_XBF_RUN_QUEUES;
+		rw = (bp->b_flags & XBF_WRITE) ? WRITE_META : READ_META;
 	} else {
 		rw = (bp->b_flags & XBF_WRITE) ? WRITE :
 		     (bp->b_flags & XBF_READ_AHEAD) ? READA : READ;

fs/xfs/linux-2.6/xfs_buf.h

@@ -55,6 +55,7 @@ typedef enum {
 	XBF_FS_MANAGED = (1 << 8),  /* filesystem controls freeing memory  */
  	XBF_ORDERED = (1 << 11),    /* use ordered writes		   */
 	XBF_READ_AHEAD = (1 << 12), /* asynchronous read-ahead		   */
+	XBF_LOG_BUFFER = (1 << 13), /* this is a buffer used for the log   */
 
 	/* flags used only as arguments to access routines */
 	XBF_LOCK = (1 << 14),       /* lock requested			   */

fs/xfs/xfs_log.c

@@ -1441,6 +1441,7 @@ xlog_sync(xlog_t		*log,
 	XFS_BUF_ZEROFLAGS(bp);
 	XFS_BUF_BUSY(bp);
 	XFS_BUF_ASYNC(bp);
+	bp->b_flags |= XBF_LOG_BUFFER;
 	/*
 	 * Do an ordered write for the log block.
 	 * Its unnecessary to flush the first split block in the log wrap case.
@@ -1478,6 +1479,7 @@ xlog_sync(xlog_t		*log,
 		XFS_BUF_ZEROFLAGS(bp);
 		XFS_BUF_BUSY(bp);
 		XFS_BUF_ASYNC(bp);
+		bp->b_flags |= XBF_LOG_BUFFER;
 		if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
 			XFS_BUF_ORDERED(bp);
 		dptr = XFS_BUF_PTR(bp);

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))