From: Jens Axboe <axboe@kernel.dk>
To: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH block/for-4.0-fixes] writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()
Date: Wed, 04 Mar 2015 08:31:51 -0700 [thread overview]
Message-ID: <54F72567.3060406@kernel.dk> (raw)
In-Reply-To: <20150304153050.GA1249@quack.suse.cz>
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@suse.cz>
We should add that it fixes c42843f2f0bbc (from 2011!) as well.
--
Jens Axboe
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WARNING: multiple messages have this Message-ID (diff)
From: Jens Axboe <axboe@kernel.dk>
To: Jan Kara <jack@suse.cz>, Tejun Heo <tj@kernel.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH block/for-4.0-fixes] writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()
Date: Wed, 04 Mar 2015 08:31:51 -0700 [thread overview]
Message-ID: <54F72567.3060406@kernel.dk> (raw)
In-Reply-To: <20150304153050.GA1249@quack.suse.cz>
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@suse.cz>
We should add that it fixes c42843f2f0bbc (from 2011!) as well.
--
Jens Axboe
next prev parent reply other threads:[~2015-03-04 15:31 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-04 15:22 [PATCH block/for-4.0-fixes] writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth() Tejun Heo
2015-03-04 15:22 ` Tejun Heo
2015-03-04 15:30 ` Jan Kara
2015-03-04 15:30 ` Jan Kara
2015-03-04 15:31 ` Jens Axboe [this message]
2015-03-04 15:31 ` Jens Axboe
2015-03-04 15:37 ` Tejun Heo
2015-03-04 15:37 ` Tejun Heo
2015-03-04 15:38 ` Jens Axboe
2015-03-04 15:38 ` Jens Axboe
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