linux-ext4 - Re: [PATCH 3/3] mke2fs: document bigalloc and cluster-size

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Message-ID: <20130115191254.GD17719@thunk.org>
Date:	Tue, 15 Jan 2013 14:12:54 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [PATCH 3/3] mke2fs: document bigalloc and cluster-size

On Mon, Jan 14, 2013 at 10:10:06PM -0500, Theodore Ts'o wrote:
> On Sun, Jan 13, 2013 at 05:08:15PM +0800, Zheng Liu wrote:
> > From: Zheng Liu <wenqing.lz@...bao.com>
> > 
> > Bigalloc feature has been used for a long time, but the documentation in mke2fs
> > is still missing.  So add it.
> > 
> > Signed-off-by: Zheng Liu <wenqing.lz@...bao.com>
> 
> Applied (with some changes to improve the english/wording).

BTW, I used the following modified text:

                   bigalloc
                          This  feature  enables clustered allocation, so that
                          the unit of allocation is a power of two  number  of
                          blocks.   That  is,  each bit in the what had tradi‐
                          tionally been known as the block  allocation  bitmap
                          now  indicates  whether  a cluster is in use or not,
                          where a cluster is by default composed of 16 blocks.
                          This  feature  can  decrease the time spent on doing
                          block allocation and brings  smaller  fragmentation,
                          especially  for large files.  The size can be speci‐
                          fied using the -C option.

                          Warning: The bigalloc feature is still under  devel‐
                          opment,  and  may  not  be fully supported with your
                          kernel or may have various bugs.  Please see the web
                          page  http://ext4.wiki.kernel.org/index.php/Bigalloc
                          for details.

And I populated the page on the ext4 wiki so that when we finally fix
the delalloc/bigalloc problem, we can update the ext4 wiki to reflect
this.

					- Ted
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