linux-kernel - Re: Re: cgroup: Fix split bio been throttled more than once

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Date:	Wed, 6 Jul 2016 23:39:29 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	aaronlee0817 <aaronlee0817@....com>, Jens Axboe <axboe@...nel.dk>,
	Ming Lin <mlin@...nel.org>, Shaohua Li <shli@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	cgroup@...r.kernel.org, jiale0817.li@...sung.com,
	yanzi.zhang@...sung.com, zhen1.zhang@...sung.com,
	linux-block <linux-block@...r.kernel.org>
Subject: Re: Re: cgroup: Fix split bio been throttled more than once

On Wed, Jul 6, 2016 at 11:06 PM, Tejun Heo <tj@...nel.org> wrote:
> Hello,
>
> On Wed, Jul 06, 2016 at 10:58:55PM +0800, aaronlee0817 wrote:
>> >But that said, can't we just copy BIO_THROTLED while splitting?
>>
>> In my opinion， copying BIO_THROTLED while splitting doesn't work
>> with this, because, the bio within the limit will not set BIO_THROTLED
>> but will be split, and back to call generic_make_request(), and will be
>> count twice.
>
> I see.  It's just a bit weird that we're marking this from clone site
> when it's an issue which is specific to throttling.  The thing is
> depending on how bio clone is used, it could misbehave in the other

The cloned bio often need to be submitted via generic_make_request().

> direction (bio not accounted at all).  What we want to know is whether
> a bio has been previously accounted or not, rather than whether a bio
> is a result of splitting.  I think it'd be better to track that
> instead.

Looks the flag of BIO_THROTLED doesn't work well, and it should have
been set if the bio is accounted, and seems not related with splitting.

Thanks,
Ming

>
> Thanks.
>
> --
> tejun
> --
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-- 
Ming Lei