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

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Date:	Wed, 04 Mar 2015 08:38:21 -0700
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>
CC:	Jan Kara <jack@...e.cz>, 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 08:37 AM, Tejun Heo wrote:
> Subject: writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()
>
> 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.
>
> Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Acked-by: Jan Kara <jack@...e.cz>
> Cc: Wu Fengguang <fengguang.wu@...el.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: stable@...r.kernel.org
> ---
> Added the "fixes" tag.  Jens, can you please route this one?

Yup will do, thanks Tejun.

-- 
Jens Axboe

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