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Reply-To: <hzhong@cisco.com>
From: "Hua Zhong" <hzhong@cisco.com>
To: "=?utf-8?Q?'J=E9=B0=8En_Engel'?=" <joern@wohnheim.fh-wedel.de>
Cc: "'Andy Isaacson'" <adi@hexapodia.org>, <linux-kernel@vger.kernel.org>
Subject: RE: Is there a "make hole" (truncate in middle) syscall?
Date: Thu, 11 Dec 2003 11:55:13 -0800
Organization: Cisco Systems
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> > Understood. Two filesystems we are using: tmpfs and ext3. For the
> > former, fragmentation doesn't matter.
> > 
> > Hey, I think when I get some cycles I can try to implement this for
> > tmpfs (since it's simpler) myself, and post a patch. :-) But before
> > that, I want to make sure it's doable.
> 
> If you really do it, please don't add a syscall for it.  Simply check
> each written page if it is completely filled with zero.  (This will be
> a very quick check for most pages, as they will contain something
> nonzero in the first couple of words)

You mean automatically punch it?

I don't think this is desirable. As someone else pointed out, "punch" might be an expensive operation and cause fragmentation (since you return the block in the middle to the fs).

I think this operation should be performed only when the application requires it.
 
> Jörn