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xfs: avoid a few disk cache flushes 

There is no need for a pre-flush when doing writing the second part of a
split log buffer, and if we are using an external log there is no need
to do a full cache flush of the log device at all given that all writes
to it use the FUA flag.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
This commit is contained in:
Christoph Hellwig 2011-07-08 14:36:36 +02:00
parent 1d5ae5dfee
commit e163cbde98
1 changed files with 12 additions and 6 deletions
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18
fs/xfs/xfs_log.c
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@ -1371,15 +1371,21 @@ xlog_sync(xlog_t *log,
bp->b_flags |= XBF_SYNCIO;
if (log->l_mp->m_flags & XFS_MOUNT_BARRIER) {
bp->b_flags |= XBF_FUA;
/*
* If we have an external log device, flush the data device
* before flushing the log to make sure all meta data
* written back from the AIL actually made it to disk
* before writing out the new log tail LSN in the log buffer.
* Flush the data device before flushing the log to make
* sure all meta data written back from the AIL actually made
* it to disk before stamping the new log tail LSN into the
* log buffer. For an external log we need to issue the
* flush explicitly, and unfortunately synchronously here;
* for an internal log we can simply use the block layer
* state machine for preflushes.
*/
if (log->l_mp->m_logdev_targp != log->l_mp->m_ddev_targp)
xfs_blkdev_issue_flush(log->l_mp->m_ddev_targp);
bp->b_flags |= XBF_FUA | XBF_FLUSH;
else
bp->b_flags |= XBF_FLUSH;
}
ASSERT(XFS_BUF_ADDR(bp) <= log->l_logBBsize-1);
@ -1414,7 +1420,7 @@ xlog_sync(xlog_t *log,
XFS_BUF_ASYNC(bp);
bp->b_flags |= XBF_SYNCIO;
if (log->l_mp->m_flags & XFS_MOUNT_BARRIER)
bp->b_flags |= XBF_FUA | XBF_FLUSH;
bp->b_flags |= XBF_FUA;
dptr = XFS_BUF_PTR(bp);
/*
* Bump the cycle numbers at the start of each block