linux-kernel - [068/102] mm/backing-dev.c: reset bdi min_ratio in bdi

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Date:	Wed, 03 Aug 2011 15:01:28 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Peter Zijlstra <peterz@...radead.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Miklos Szeredi <miklos@...redi.hu>
Subject: [068/102] mm/backing-dev.c: reset bdi min_ratio in bdi_unregister()

3.0-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Peter Zijlstra <peterz@...radead.org>

commit ccb6108f5b0b541d3eb332c3a73e645c0f84278e upstream.

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@...radead.org>
Reported-by: Vito Caputo <lkml@...garu.com>
Cc: Wu Fengguang <fengguang.wu@...el.com>
Cc: Miklos Szeredi <miklos@...redi.hu>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 mm/backing-dev.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -606,6 +606,7 @@ static void bdi_prune_sb(struct backing_
 void bdi_unregister(struct backing_dev_info *bdi)
 {
 	if (bdi->dev) {
+		bdi_set_min_ratio(bdi, 0);
 		trace_writeback_bdi_unregister(bdi);
 		bdi_prune_sb(bdi);
 		del_timer_sync(&bdi->wb.wakeup_timer);

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