mm/backing-dev.c: reset bdi min_ratio in bdi_unregister()

[ 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@infradead.org>
Reported-by: Vito Caputo <lkml@pengaru.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c0f7157198292fed911471958ff49c09554a49c1..3f2b8d037c98cc164efccd0b278d8d193eaa9c4b 100644 (file)
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -646,6 +646,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
 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))