linux-kernel - Re: How to handle >16TB devices on 32 bit hosts ??

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Message-Id: <20090722115155.f99dcf76.akpm@linux-foundation.org>
Date:	Wed, 22 Jul 2009 11:51:55 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andreas Dilger <adilger@....com>
Cc:	neilb@...e.de, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
	dm-devel@...hat.com
Subject: Re: How to handle >16TB devices on 32 bit hosts ??

On Wed, 22 Jul 2009 12:32:44 -0600
Andreas Dilger <adilger@....com> wrote:

> On Jul 21, 2009  23:59 -0700, Andrew Morton wrote:
> > On Sat, 18 Jul 2009 10:08:10 +1000 Neil Brown <neilb@...e.de> wrote:
> > I expect that the VFS could be made to work with 64-bit pgoff_t fairly
> > easily.  The generated code will be pretty damn sad.
> > 
> > radix-trees use a ulong index, so we would need a new
> > lib/radix_tree64.c or some other means of fixing that up.
> > 
> > The bigger problem is filesystems - they'll each need to be checked,
> > tested, fixed and enabled.  It's probably not too bad for the
> > mainstream filesystems which mostly bounce their operations into VFS
> > libarary functions anyway.
> 
> I don't think this is a primary concern for most filesystems even today.
> Filesystems that work correctly > 16TB on 64-bit platforms should continue
> to work correctly on 32-bit platforms.

Not if they use an unsigned long to hold a pagecache index anywhere.

akpm:/usr/src/25> grep 'unsigned long' fs/*/*.c | wc -l
3465
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