[PATCH] [3/50] mm/backing-dev.c: reset bdi min_ratio in bdi_unregister()

[Andi Kleen]

2.6.35-longterm review patch.  If anyone has any objections, please let me know.

------------------
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

[ upstream commit ccb6108f5b0b541d3eb332c3a73e645c0f84278e ]

Vito said:

: The system has many usb disks coming and going day to day, with their
: respective bdi's having min_ratio set to 1 when inserted.  It works for
: some time until eventually min_ratio can no longer be set, even when the
: active set of bdi's seen in /sys/class/bdi/*/min_ratio doesn't add up to
: anywhere near 100.
:
: This then leads to an unrelated starvation problem caused by write-heavy
: fuse mounts being used atop the usb disks, a problem the min_ratio setting
: at the underlying devices bdi effectively prevents.

Fix this leakage by resetting the bdi min_ratio when unregistering the
BDI.

Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Reported-by: Vito Caputo <lkml@xxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

Index: linux-2.6.35.y/mm/backing-dev.c
===================================================================
--- linux-2.6.35.y.orig/mm/backing-dev.c
+++ linux-2.6.35.y/mm/backing-dev.c
@@ -646,6 +646,7 @@ static void bdi_prune_sb(struct backing_
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
+		bdi_set_min_ratio(bdi, 0);
 		bdi_prune_sb(bdi);
 
 		if (!bdi_cap_flush_forker(bdi))
--
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