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Date:	Wed, 18 Apr 2012 09:57:10 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger@...mcloud.com>
CC:	Zheng Liu <gnehzuil.liu@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Zheng Liu <wenqing.lz@...bao.com>
Subject: Re: [RFC][PATCH 0/3] add FALLOC_FL_NO_HIDE_STALE flag in fallocate

On 4/17/12 11:59 PM, Andreas Dilger wrote:

...

> Secondly, your test program is not doing random writes to disk, but
> rather doing writes at 64kB intervals. There is logic in the
> uninitialized extent handling that will write zeros to an entire
> extent, rather than create many fragmented uninitialized extents.  It
> may be possible that you are zeroing out the entire file, and writing
> 16x as much data as you expect.
> 
> Cheers, Andreas

I don't think the testcase as written is triggering that behavior, though
other similar testcases might.  In this case the left-over uninit extents
are large enough that they don't get zeroed:

File size of /mnt/scratch/test is 268435456 (65536 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0    34816               1 
   1       1    34817              15 unwritten
   2      16    34832               1 
   3      17    34833              15 unwritten
   4      32    34848               1 
   5      33    34849              15 unwritten
...

Good guess though :)

-Eric
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