linux-kernel - Re: [PATCH block/for-4.0-fixes] writeback: add missing INITIAL_JIFFIES init in global_update

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Message-ID: <54F72567.3060406@kernel.dk>
Date:	Wed, 04 Mar 2015 08:31:51 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>
CC:	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH block/for-4.0-fixes] writeback: add missing INITIAL_JIFFIES
 init in global_update_bandwidth()

On 03/04/2015 08:30 AM, Jan Kara wrote:
> On Wed 04-03-15 10:22:43, Tejun Heo wrote:
>> global_update_bandwidth() uses static variable update_time as the
>> timestamp for the last update but forgets to initialize it to
>> INITIALIZE_JIFFIES.
>>
>> This means that global_dirty_limit will be 5 mins into the future on
>> 32bit and some large amount jiffies into the past on 64bit.  This
>> isn't critical as the only effect is that global_dirty_limit won't be
>> updated for the first 5 mins after booting on 32bit machines,
>> especially given the auxiliary nature of global_dirty_limit's role -
>> protecting against global dirty threshold's sudden dips; however, it
>> does lead to unintended suboptimal behavior.  Fix it.
>    Looks good. You can add:
> Reviewed-by: Jan Kara <jack@...e.cz>

We should add that it fixes c42843f2f0bbc (from 2011!) as well.

-- 
Jens Axboe

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