linux-kernel - Re: [PATCH block/for-4.7-fixes] writeback: use higher precision calculation in domain_dirty

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Message-ID: <574C544E.70905@kernel.dk>
Date:	Mon, 30 May 2016 08:55:10 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>, Jan Kara <jack@...e.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, Miao Xie <miaoxie@...wei.com>,
	kernel-team@...com
Subject: Re: [PATCH block/for-4.7-fixes] writeback: use higher precision
 calculation in domain_dirty_limits()

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@...nel.org>
> Reported-by: Miao Xie <miaoxie@...wei.com>
> Link: http://lkml.kernel.org/g/57333E75.3080309@huawei.com
> Cc: stable@...r.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