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Re: [PATCH] xfstests 255: add a seek_data/seek_hole tester

To: Pádraig Brady <P@xxxxxxxxxxxxxx>
Subject: Re: [PATCH] xfstests 255: add a seek_data/seek_hole tester
From: Sunil Mushran <sunil.mushran@xxxxxxxxxx>
Date: Wed, 29 Jun 2011 10:29:02 -0700
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Josef Bacik <josef@xxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <4E0B019E.8080800@xxxxxxxxxxxxxx>
References: <1309275199-10801-1-git-send-email-josef@xxxxxxxxxx> <1309275199-10801-5-git-send-email-josef@xxxxxxxxxx> <20110629065306.GC1026@dastard> <20110629074021.GA26086@xxxxxxxxxxxxx> <4E0B019E.8080800@xxxxxxxxxxxxxx>
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On 06/29/2011 03:42 AM, Pádraig Brady wrote:
There is the argument, that if this interface can distinguish
these dirty unwritten extents, then why can't the fiemap interface too?
The advantage of the fiemap interface is that it can distinguish
empty extents vs holes. Empty extents will become increasingly common
I think, given the fragmentation and space guarantee benefits they give.
It would be cool for cp for example to be able to efficiently copy
empty extents from source to dest.

I'm not too sure about that. Atleast not enabled by default. Most users
use cp to backup data. Not empty space. In this case, this empty extent
may not even be de-dupable.

Frankly I'd be happier of cp started to exploited fallocate() to create larger
extents before copying data into them. Atleast for the large files.

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