tree 2ace993dd54bb6dd94fdd4c0cb03813c6bf4c6a3
parent 4434c33c7f233a7ee5dcaf357fbf795818ea8861
author Chris Mason <chris.mason@oracle.com> 1222282290 -0400
committer Chris Mason <chris.mason@oracle.com> 1222371719 -0400

Btrfs: Raise thresholds for metadata writeback

Btrfs metadata writeback is fairly expensive.  Once a tree block is written
it must be cowed before it can be changed again.  The btree writepages
code has a threshold based on a count of dirty btree bytes which is
updated as IO is sent out.

This changes btree_writepages to skip the writeout if there are less
than 32MB of dirty bytes from the btrees, improving performance
across many workloads.

Signed-off-by: Chris Mason <chris.mason@oracle.com>