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Re: [PATCH 4/7][TAKE5] support new modes in fallocate

To: David Chinner <dgc@xxxxxxx>
Subject: Re: [PATCH 4/7][TAKE5] support new modes in fallocate
From: Nathan Scott <nscott@xxxxxxxxxx>
Date: Thu, 28 Jun 2007 10:53:08 +1000
Cc: Andreas Dilger <adilger@xxxxxxxxxxxxx>, xfs-oss <xfs@xxxxxxxxxxx>, "Amit K. Arora" <aarora@xxxxxxxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, suparna@xxxxxxxxxx, cmm@xxxxxxxxxx
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On Thu, 2007-06-28 at 10:39 +1000, David Chinner wrote:
> 
> 
> I don't think it does - swapfile I/O looks like it goes direct to
> bio without passing through the filesystem.  When the swapfile is
> mapped, it scans and records the extent map of the entire swapfile
> in a separate structure and AFAICT the swap code uses that built map
> without touching the filesystem at all.
> 
> If that is true then the written/unwritten state of the extents is
> irrelevant; all we need is allocated disk space for the file and
> swapping should work. And it's not like anyone should be reading
> the contents of that swapfile through the filesystem, either. ;)

Ah, yes, good point - thats true.  Unwritten extents are ideal for
this then, as attempts to read swap via the regular interfaces will
return zeros instead of random swapped out memory contents.

cheers.


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