commit 3310225dfc71a35a2cc9340c15c0e08b14b3c754 upstream.

PROP_MAX_SHIFT should be set to <=32 on 64-bit box. This fixes two bugs
in the below lines of bdi_dirty_limit():

	bdi_dirty *= numerator;
	do_div(bdi_dirty, denominator);

1) divide error: do_div() only uses the lower 32 bit of the denominator,
   which may trimmed to be 0 when PROP_MAX_SHIFT > 32.

2) overflow: (bdi_dirty * numerator) could easily overflow if numerator
   used up to 48 bits, leaving only 16 bits to bdi_dirty

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: Ilya Tumaykin <librarian_rus@yahoo.com>
Tested-by: Ilya Tumaykin <librarian_rus@yahoo.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

reorder structure to remove 8 bytes of padding on 64 bit builds

(also removes 8 bytes from task_struct)

Signed-off-by: Richard Kennedy <richard@rsk.demon.co.uk>
Cc: peterz@infradead.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

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>

Given a set of objects, floating proportions aims to efficiently give the
proportional 'activity' of a single item as compared to the whole set. Where
'activity' is a measure of a temporal property of the items.

It is efficient in that it need not inspect any other items of the set
in order to provide the answer. It is not even needed to know how many
other items there are.

It has one parameter, and that is the period of 'time' over which the
'activity' is measured.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>