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mm: bdi: allow setting a minimum for the bdi dirty limit

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Under normal circumstances each device is given a part of the total write-back
cache that relates to its current avg writeout speed in relation to the other
devices.

min_ratio - allows one to assign a minimum portion of the write-back cache to
a particular device.  This is useful in situations where you might want to
provide a minimum QoS.  (One request for this feature came from flash based
storage people who wanted to avoid writing out at all costs - they of course
needed some pdflush hacks as well)

max_ratio - allows one to assign a maximum portion of the dirty limit to a
particular device.  This is useful in situations where you want to avoid one
device taking all or most of the write-back cache.  Eg.  an NFS mount that is
prone to get stuck, or a FUSE mount which you don't trust to play fair.

Add "min_ratio" to /sys/class/bdi.  This indicates the minimum percentage of
the global dirty threshold allocated to this bdi.

[mszeredi@suse.cz]

 - fix parsing in min_ratio_store()
 - document new sysfs attribute

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Peter Zijlstra 2008-04-30 00:54:35 -07:00 • committed by Linus Torvalds
parent b6f2fcbcfc
commit 189d3c4a94
4 changed files with 57 additions and 1 deletions
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4
include/linux/backing-dev.h
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@ -51,6 +51,8 @@ struct backing_dev_info {
struct prop_local_percpu completions;
int dirty_exceeded;
unsigned int min_ratio;
struct device *dev;
};
@ -137,6 +139,8 @@ static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
#endif
}
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
/*
* Flags in backing_dev_info::capability
* - The first two flags control whether dirty pages will contribute to the