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-rw-r--r--Documentation/block/queue-sysfs.txt7
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/block/queue-sysfs.txt b/Documentation/block/queue-sysfs.txt
index 2a3904030dea..87abf1ac2939 100644
--- a/Documentation/block/queue-sysfs.txt
+++ b/Documentation/block/queue-sysfs.txt
@@ -169,5 +169,12 @@ This is the number of bytes the device can write in a single write-same
command. A value of '0' means write-same is not supported by this
device.
+wb_lat_usec (RW)
+----------------
+If the device is registered for writeback throttling, then this file shows
+the target minimum read latency. If this latency is exceeded in a given
+window of time (see wb_window_usec), then the writeback throttling will start
+scaling back writes.
+
Jens Axboe <jens.axboe@oracle.com>, February 2009