A barrier request should by defintion have priority in get_request
and let the queue be unplugged immediately as it's blocking all forward
progress due to the queue draining.
Most filesystems already get this implicitly by the way how submit_bh
treats the buffer_ordered flag, and gfs2 sets it explicitly. But btrfs
and XFS are still forgetting to set the flag, as is blkdev_issue_flush
and some places in DM/MD.
For XFS on metadata heavy workloads this gives a consistent speedup
in the 2-3% range.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Index: linux-2.6/include/linux/fs.h
===================================================================
--- linux-2.6.orig/include/linux/fs.h 2010-06-17 08:37:05.238025121 +0200
+++ linux-2.6/include/linux/fs.h 2010-06-17 08:37:27.967253715 +0200
@@ -136,7 +136,7 @@ struct inodes_stat_t {
* SWRITE_SYNC
* SWRITE_SYNC_PLUG Like WRITE_SYNC/WRITE_SYNC_PLUG, but locks the buffer.
* See SWRITE.
- * WRITE_BARRIER Like WRITE, but tells the block layer that all
+ * WRITE_BARRIER Like WRITE_SYNC, but tells the block layer that all
* previously submitted writes must be safely on storage
* before this one is started. Also guarantees that when
* this write is complete, it itself is also safely on
@@ -159,7 +159,7 @@ struct inodes_stat_t {
#define SWRITE_SYNC_PLUG \
(SWRITE | (1 << BIO_RW_SYNCIO) | (1 << BIO_RW_NOIDLE))
#define SWRITE_SYNC (SWRITE_SYNC_PLUG | (1 << BIO_RW_UNPLUG))
-#define WRITE_BARRIER (WRITE | (1 << BIO_RW_BARRIER))
+#define WRITE_BARRIER (WRITE_SYNC | (1 << BIO_RW_BARRIER))
/*
* These aren't really reads or writes, they pass down information about
Index: linux-2.6/fs/gfs2/log.c
===================================================================
--- linux-2.6.orig/fs/gfs2/log.c 2010-06-17 08:42:18.020253855 +0200
+++ linux-2.6/fs/gfs2/log.c 2010-06-17 08:42:54.135032427 +0200
@@ -595,7 +595,7 @@ static void log_write_header(struct gfs2
if (test_bit(SDF_NOBARRIERS, &sdp->sd_flags))
goto skip_barrier;
get_bh(bh);
- submit_bh(WRITE_SYNC | (1 << BIO_RW_BARRIER) | (1 << BIO_RW_META), bh);
+ submit_bh(WRITE_BARRIER | (1 << BIO_RW_META), bh);
wait_on_buffer(bh);
if (buffer_eopnotsupp(bh)) {
clear_buffer_eopnotsupp(bh);
--
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