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What: /sys/class/bdi/<bdi>/
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
setting and retrieving various BDI specific variables.
The <bdi> identifier can be either of the following:
MAJOR:MINOR
Device number for block devices, or value of st_dev on
non-block filesystems which provide their own BDI, such as NFS
and FUSE.
MAJOR:MINOR-fuseblk
Value of st_dev on fuseblk filesystems.
default
The default backing dev, used for non-block device backed
filesystems which do not provide their own BDI.
Files under /sys/class/bdi/<bdi>/
---------------------------------
read_ahead_kb (read-write)
Size of the read-ahead window in kilobytes
min_ratio (read-write)
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)
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.
stable_pages_required (read-only)
If set, the backing device requires that all pages comprising a write
request must not be changed until writeout is complete.
strictlimit (read-write)
Forces per-BDI checks for the share of given device in the write-back
cache even before the global background dirty limit is reached. This
is useful in situations where the global limit is much higher than
affordable for given relatively slow (or untrusted) device. Turning
strictlimit on has no visible effect if max_ratio is equal to 100%.
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