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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: [PATCH] rd: Use a private inode for backing storage
Date: Sun, 21 Oct 2007 14:28:55 +1000
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Cc: Christian Borntraeger <borntraeger@de.ibm.com>,
       Andrew Morton <akpm@linux-foundation.org>, 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 08:51, Eric W. Biederman wrote:
> Currently the ramdisk tries to keep the block device page cache pages
> from being marked clean and dropped from memory.  That fails for
> filesystems that use the buffer cache because the buffer cache is not
> an ordinary buffer cache user and depends on the generic block device
> address space operations being used.
>
> To fix all of those associated problems this patch allocates a private
> inode to store the ramdisk pages in.
>
> The result is slightly more memory used for metadata, an extra copying
> when reading or writing directly to the block device, and changing the
> software block size does not loose the contents of the ramdisk.  Most
> of all this ensures we don't loose data during normal use of the
> ramdisk.
>
> I deliberately avoid the cleanup that is now possible because this
> patch is intended to be a bug fix.

This just breaks coherency again like the last patch. That's a
really bad idea especially for stable (even if nothing actually
was to break, we'd likely never know about it anyway).

Christian's patch should go upstream and into stable. For 2.6.25-6,
my rewrite should just replace what's there. Using address spaces
to hold the ramdisk pages just confuses the issue even if they
*aren't* actually wired up to the vfs at all. Saving 20 lines is
not a good reason to use them.

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