linux-kernel - Re: [PATCH V4 05/15] blk-throttle: add downgrade logic

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Message-ID: <20161122233824.GD14628@shli-mbp.local>
Date:   Tue, 22 Nov 2016 15:38:24 -0800
From:   Shaohua Li <shli@...com>
To:     Tejun Heo <tj@...nel.org>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <Kernel-team@...com>, <axboe@...com>, <vgoyal@...hat.com>
Subject: Re: [PATCH V4 05/15] blk-throttle: add downgrade logic

On Tue, Nov 22, 2016 at 04:42:00PM -0500, Tejun Heo wrote:
> Hello,
> 
> On Tue, Nov 22, 2016 at 04:21:21PM -0500, Tejun Heo wrote:
> > 1. A cgroup and its high and max limits don't have much to do with
> >    other cgroups and their limits.  I don't get how the choice between
> >    high and max limits can be a td-wide state.
> 
> Ah, okay, this combines with idle cgroup detection to determine
> whether the cgroups should be allowed to exceed high limits.  It makes
> more sense to me now.  In that case, for the high/max limit range
> issues, the enforced high/max limits can simply follow what's implied
> by the configuration.  e.g. if high=100 max=80, just behave as if both
> high and max are 80.
> 
> > 2. Comparing parent's and child's limits and saying that either can be
> >    ignored because one is higher than the other isn't correct.  A
> >    parent's limit doesn't apply to each child separately.  It has to
> >    be aggregated.  e.g. you can ignore a parent's setting if the sum
> >    of all children's limits is smaller than the parent's but then
> >    again there could still be a lower limit higher up the tree, so
> >    they would still have to be examined.
> 
> This part still seems weird tho.  What am I misunderstanding?

You are right, the checks are unncessary. I'll delete them.

Thanks,
Shaohua