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

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

[mszeredi@suse.cz]

 - fix parsing in max_ratio_store().
 - export bdi_set_max_ratio() to modules
 - limit bdi_dirty with bdi->max_ratio
 - 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>

1 files changed, 8 insertions, 1 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index b9e8a9368dc6..c55e811ca180 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -49,4 +49,11 @@ 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.
-        The default is zero
+        If min_ratio would become larger than the current max_ratio,
+        then also EINVAL is returned.  The default is zero
+
+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