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Commit e163cbde authored by Christoph Hellwig's avatar Christoph Hellwig
Browse files

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: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarAlex Elder <aelder@sgi.com>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
parent 1d5ae5df

fs/xfs/xfs_log.c

+12 −6
Original line number Diff line number Diff line
@@ -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