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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [RFC][PATCH] block: Isolate the buffer cache in it's own mappings.
Date: Sun, 21 Oct 2007 14:24:46 +1000
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Cc: Andrew Morton <akpm@linux-foundation.org>,
       Chris Mason <chris.mason@oracle.com>,
       Christian Borntraeger <borntraeger@de.ibm.com>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org,
       Martin Schwidefsky <schwidefsky@de.ibm.com>,
       "Theodore Ts'o" <tytso@mit.edu>, stable@kernel.org
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On Saturday 20 October 2007 07:27, Eric W. Biederman wrote:
> Andrew Morton <akpm@linux-foundation.org> writes:
> > I don't think we little angels want to tread here.  There are so many
> > weirdo things out there which will break if we bust the coherence between
> > the fs and /dev/hda1.
>
> We broke coherence between the fs and /dev/hda1 when we introduced
> the page cache years ago,

Not for metadata. And I wouldn't expect many filesystem analysis
tools to care about data.


> and weird hacky cases like 
> unmap_underlying_metadata don't change that.

unmap_underlying_metadata isn't about raw block device access at
all, though (if you write to the filesystem via the blockdevice
when it isn't expecting it, it's going to blow up regardless).


> Currently only 
> metadata is more or less in sync with the contents of /dev/hda1.

It either is or it isn't, right? And it is, isn't it? (at least
for the common filesystems).
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