Re: [PATCH block/for-4.7-fixes] writeback: use higher precision calculation in domain_dirty_limits()

From	Jens Axboe <axboe@kernel.dk>
Newsgroups	linux.kernel
Subject	Re: [PATCH block/for-4.7-fixes] writeback: use higher precision calculation in domain_dirty_limits()
Date	2016-05-30 17:00 +0200
Message-ID	<rEwPD-5wp-7@gated-at.bofh.it> (permalink)
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On 05/27/2016 12:34 PM, Tejun Heo wrote:
> As vm.dirty_[background_]bytes can't be applied verbatim to multiple
> cgroup writeback domains, they get converted to percentages in
> domain_dirty_limits() and applied the same way as
> vm.dirty_[background]ratio.  However, if the specified bytes is lower
> than 1% of available memory, the calculated ratios become zero and the
> writeback domain gets throttled constantly.
>
> Fix it by using per-PAGE_SIZE instead of percentage for ratio
> calculations.  Also, the updated DIV_ROUND_UP() usages now should
> yield 1/4096 (0.0244%) as the minimum ratio as long as the specified
> bytes are above zero.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Miao Xie <miaoxie@huawei.com>
> Link: http://lkml.kernel.org/g/57333E75.3080309@huawei.com
> Cc: stable@vger.kernel.org # v4.2+
> Fixes: 9fc3a43e1757 ("writeback: separate out domain_dirty_limits()")

Queued up for this series, with the minor comment tweak that Jan suggested.

-- 
Jens Axboe

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Re: [BUG]Writeback Cgroup/Dirty Throttle: very small buffered write  thoughput caused by writeback cgroup and dirty thottle Tejun Heo <tj@kernel.org> - 2016-05-12 20:10 +0200
  Re: [BUG]Writeback Cgroup/Dirty Throttle: very small buffered write  thoughput caused by writeback cgroup and dirty thottle Miao Xie <miaoxie@huawei.com> - 2016-05-13 08:20 +0200
    Re: [BUG]Writeback Cgroup/Dirty Throttle: very small buffered write  thoughput caused by writeback cgroup and dirty thottle Tejun Heo <tj@kernel.org> - 2016-05-27 20:30 +0200
  [PATCH block/for-4.7-fixes] writeback: use higher precision  calculation in domain_dirty_limits() Tejun Heo <tj@kernel.org> - 2016-05-27 20:40 +0200
    Re: [PATCH block/for-4.7-fixes] writeback: use higher precision  calculation in domain_dirty_limits() Jan Kara <jack@suse.cz> - 2016-05-30 10:10 +0200
    Re: [PATCH block/for-4.7-fixes] writeback: use higher precision  calculation in domain_dirty_limits() Jens Axboe <axboe@kernel.dk> - 2016-05-30 17:00 +0200

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