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

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Date:	Mon, 24 Sep 2012 11:35:09 +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 02:41:14PM -0400, Theodore Ts'o wrote:
> On Wed, Aug 22, 2012 at 02:05:39PM +0800, Zheng Liu wrote:
> > + * Extents status encompass delayed extents and extent locks
> 
> I've looked over this patch set, and as near as I can tell, we aren't
> (yet) using the extents status structure to do extent-level locking.
> I could imagine using that in the future so we aren't using i_data_sem
> to lock out the entire tree, so block allocations could happen in
> parallel, but that's not here yet.
> 
> Is there something I'm missing, or was something else meant by "extent
> locks" here?

Hi Ted,

In my plan, the first step for extent status tree is only to record
delay extent in memory.  It can simplify the implementation of fiemap
and bigalloc, and introduce lseek SEEK_DATA/SEEK_HOLE support.  That is
all I want to finish in first step.  I am very glad to see that these
patches has been applied into dev branch even though it still has some
problems.  I will look at these problem ASAP.

Indeed, in this patch set, extent-level locking is still not used
because that is my next step in my plan [1].  I will try to use it
after these patches are fully tested and applied.  Thanks.

1. http://www.spinics.net/lists/linux-fsdevel/msg56291.html

Regards,
Zheng
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