linux-kernel - Re: [PATCH v2] writeback: avoid race when update bandwidth

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Message-ID: <20120613035920.GV22848@dastard>
Date:	Wed, 13 Jun 2012 13:59:20 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Wanpeng Li <liwp.linux@...il.com>, linux-kernel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>
Subject: Re: [PATCH v2] writeback: avoid race when update bandwidth

On Tue, Jun 12, 2012 at 07:52:19PM +0800, Fengguang Wu wrote:
> On Tue, Jun 12, 2012 at 07:46:01PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <liwp@...ux.vnet.ibm.com>
> > 
> > "V1 -> V2"
> > * remove dirty_lock
> > 
> > Since bdi->wb.list_lock is used to protect the b_* lists,
> > so the flushers who call wb_writeback to writeback pages will
> > stuck when bandwidth update policy holds this lock. In order
> > to avoid this race we can introduce a new bandwidth_lock who
> > is responsible for protecting bandwidth update policy.
> > 
> > Signed-off-by: Wanpeng Li <liwp.linux@...il.com>
> 
> Applied with a new title "writeback: use a standalone lock for
> updating write bandwidth". "race" is sensitive because it often
> refers to some locking error.

Fengguang - can we get some evidence that this is a contended lock
before changing the scope of it? All of the previous "breaking up
global locks" have been done based on lock contention data, so
moving back to a global lock for this needs to have the same
analysis provided...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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