linux-ext4 - Re: [PATCH 2/8 v3] ext4: add operations on extent status tree

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Message-ID: <20121109022255.GA27826@gmail.com>
Date:	Fri, 9 Nov 2012 10:22:55 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, jeff.liu@...cle.com, hughd@...gle.com,
	xiaoqiangnk@...il.com, achender@...ux.vnet.ibm.com,
	lczerner@...hat.com, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 2/8 v3] ext4: add operations on extent status tree

On Thu, Nov 08, 2012 at 06:21:23PM -0500, Theodore Ts'o wrote:
> On Fri, Oct 26, 2012 at 09:23:39PM +0800, Zheng Liu wrote:
> > + * 3. performance analysis
> > + *   --	overhead
> > + *	1. Apart from operations on a delayed extent tree, we need to
> > + *	down_write(inode->i_data_sem) in delayed write path to maintain delayed
> > + *	extent tree, this can have impact on parallel read-write and write-write
> 
> Hi Zheng,
> 
> I can fix this up, before I finalize your commit, but I just want to
> check.  I believe this comment is out of date --- we are now using a
> r/w spinlock, i_es_lock, yes?  Since we never hold the spinlock for
> very long, I would be surprised if this is going to be a scalability
> bottleneck (too bad Eric doesn't have access to the big SMP machine
> that he used to use to help us do our scalability testing, so we could
> check to be sure).

Hi Ted,

Oops, it is my fault.  Indeed it needs to be replaced with i_es_lock.  I
can do some tests in a server which has 16 cores, but I am afraid that
it is not so big as you thought.  I am willing to run Eric's tests to 
ensure that there is no any scalability problem.
 
Regards,
Zheng
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