From: Peter Staubach <staubach@redhat.com>
To: Kenny Simpson <theonetruekenny@yahoo.com>
Cc: linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: nfs question - ftruncate vs pwrite
Date: Wed, 07 Dec 2005 16:14:11 -0500 [thread overview]
Message-ID: <439750A3.2030805@redhat.com> (raw)
In-Reply-To: <20051207204612.70808.qmail@web34114.mail.mud.yahoo.com>
Kenny Simpson wrote:
>Sorry about the previous partial message...
>
>If a file is extended via ftruncate, the new empty pages are read in before the the ftruncate
>returns (taking 64mS on my machine), but if the file is extended via pwrite, nothing is read in
>and the system call is very quick (34uS).
>
>Why is there such a difference? Is there another cheap way to grow a file and map in its new
>pages? Am I missing some other semantic difference between ftruncate and a pwrite past the end of
>the file?
>
You might use tcpdump or etherreal to see what the different traffic looks
like. I suspect that ftruncate() leads a SETATTR operation while pwrite()
leads to a WRITE operation.
ps
next prev parent reply other threads:[~2005-12-07 21:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-07 20:46 nfs question - ftruncate vs pwrite Kenny Simpson
2005-12-07 21:14 ` Peter Staubach [this message]
2005-12-07 21:50 ` Kenny Simpson
2005-12-08 4:53 ` Trond Myklebust
2005-12-08 5:00 ` Trond Myklebust
2005-12-08 16:15 ` Kenny Simpson
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