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Message-ID: <4F8ED646.1040100@redhat.com>
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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