linux-ext4 - Re: [RFC][PATCH 2/8 v2] ext4: add operations on extent status tree

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Message-ID: <20120924042512.GC6196@gmail.com>
Date:	Mon, 24 Sep 2012 12:25:12 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Lukas Czerner <lczerner@...hat.com>,
	Yongqiang Yang <xiaoqiangnk@...il.com>,
	Allison Henderson <achender@...ux.vnet.ibm.com>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [RFC][PATCH 2/8 v2] ext4: add operations on extent status tree

On Wed, Sep 19, 2012 at 02:34:52PM -0400, Theodore Ts'o wrote:
> On Wed, Aug 22, 2012 at 02:05:39PM +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
> 
> I'm working on going through this patch set now, and I'm not sure this
> is worth holding back on this patch series, but I am really concerned
> about the performance impact of this....  it would definitely show up
> on some of the scalability testing that Eric Whitney had been doing,
> for example.

Sorry, maybe I miss some mails.  Could you please tell me where I can
find Eric's mail.  Thanks.

> 
> Given that operations on the delayed extent tree should be fast,
> instead of using a mutex, any reason why we can't just add a new
> spinlock (I'm not even sure we need a rw_spinlock here) to the
> ext4_inode_info structure and use that to serialize operations on the
> delayed extent tree?

Thanks for your comment.  I will fix it.

Regards,
Zheng
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