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-rw-r--r--Documentation/ABI/testing/sysfs-class-bdi43
1 files changed, 15 insertions, 28 deletions
diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index c55e811ca180..5ac1e01bbd48 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -3,8 +3,8 @@ Date: January 2008
Contact: Peter Zijlstra <a.p.zijlstra@chello.nl>
Description:
-Provide a place in sysfs for the backing_dev_info object.
-This allows us to see and set the various BDI specific variables.
+Provide a place in sysfs for the backing_dev_info object. This allows
+setting and retrieving various BDI specific variables.
The <bdi> identifier can be either of the following:
@@ -26,34 +26,21 @@ read_ahead_kb (read-write)
Size of the read-ahead window in kilobytes
-reclaimable_kb (read-only)
-
- Reclaimable (dirty or unstable) memory destined for writeback
- to this device
-
-writeback_kb (read-only)
-
- Memory currently under writeback to this device
-
-dirty_kb (read-only)
-
- Global threshold for reclaimable + writeback memory
-
-bdi_dirty_kb (read-only)
-
- Current threshold on this BDI for reclaimable + writeback
- memory
-
min_ratio (read-write)
- Minimal percentage of global dirty threshold allocated to this
- bdi. If the value written to this file would make the the sum
- of all min_ratio values exceed 100, then EINVAL is returned.
- If min_ratio would become larger than the current max_ratio,
- then also EINVAL is returned. The default is zero
+ Under normal circumstances each device is given a part of the
+ total write-back cache that relates to its current average
+ writeout speed in relation to the other devices.
+
+ The 'min_ratio' parameter allows assigning a minimum
+ percentage of the write-back cache to a particular device.
+ For example, this is useful for providing a minimum QoS.
max_ratio (read-write)
- Maximal percentage of global dirty threshold allocated to this
- bdi. If max_ratio would become smaller than the current
- min_ratio, then EINVAL is returned. The default is 100
+ Allows limiting a particular device to use not more than the
+ given percentage of the write-back cache. This is useful in
+ situations where we want to avoid one device taking all or
+ most of the write-back cache. For example in case of an NFS
+ mount that is prone to get stuck, or a FUSE mount which cannot
+ be trusted to play fair.