[PATCH] md: increase the delay before marking metadata clean, and make it configurable

When a md array has been idle (no writes) for 20msecs it is marked as 'clean'.
 This delay turns out to be too short for some real workloads.  So increase it
to 200msec (the time to update the metadata should be a tiny fraction of that)
and make it sysfs-configurable.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 03a13c462cf2..b19978e035fc 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -207,6 +207,15 @@ All md devices contain:
      available.  It will then appear at md/dev-XXX (depending on the
      name of the device) and further configuration is then possible.
 
+   safe_mode_delay
+     When an md array has seen no write requests for a certain period
+     of time, it will be marked as 'clean'.  When another write
+     request arrive, the array is marked as 'dirty' before the write
+     commenses.  This is known as 'safe_mode'.
+     The 'certain period' is controlled by this file which stores the
+     period as a number of seconds.  The default is 200msec (0.200).
+     Writing a value of 0 disables safemode.
+
    sync_speed_min
    sync_speed_max
      This are similar to /proc/sys/dev/raid/speed_limit_{min,max}