From 670ce93fef93bba8c8a422a79747385bec8e846a Mon Sep 17 00:00:00 2001
From: Dave Chinner <dchinner@redhat.com>
Date: Fri, 30 Sep 2011 04:45:03 +0000
Subject: [PATCH] xfs: reduce the number of log forces from tail pushing

The AIL push code will issue a log force on ever single push loop
that it exits and has encountered pinned items. It doesn't rescan
these pinned items until it revisits the AIL from the start. Hence
we only need to force the log once per walk from the start of the
AIL to the target LSN.

This results in numbers like this:

	xs_push_ail_flush.....         1456
	xs_log_force.........          1485

For an 8-way 50M inode create workload - almost all the log forces
are coming from the AIL pushing code.

Reduce the number of log forces by only forcing the log if the
previous walk found pinned buffers. This reduces the numbers to:

	xs_push_ail_flush.....          665
	xs_log_force.........           682

For the same test.

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