[PATCH 0/2] blk-throttle: simplify logic by token bucket algorithm

[Hong Zhiguo <honkiko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

From: Hong Zhiguo <zhiguohong-1Nz4purKYjRBDgjK7y7TUQ@public.gmane.org>

Based on the discussion with Vivek, Tejun and Jens.

Patch 1/2 implements basic token bucket rate limiting for blk-throttle.
Patch 2/2 adjusts some behavior for the cases pointed out by Vivek:
	- A huge bio may be allowed immediately after a long time of idle
	- When token is trimmed for above case, should not trim ancestors
	  when bio climbs up, instead, trim ancestors when bio is queued
	  on lowest child group.

Trimming of iops token is not necessary. Since a bio always costs _one_ 
iops token. Trimming it won't change the fact that current iops token is
zero or not.

Thanks Vivek for the ancestor over-trim issue and the proposed solution.
I took another method inspired by Vivek's comments but I think more decent.
Please help to review it.

Hong Zhiguo (2):
  blk-throttle: simplify logic by token bucket algorithm
  blk-throttle: trim tokens generated for an idle tree

 block/blk-throttle.c | 314 ++++++++++++++-------------------------------------
 1 file changed, 84 insertions(+), 230 deletions(-)

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1.8.1.2