linux-kernel - Re: [patch 1/3] add the fsblock layer

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Date:	Tue, 26 Jun 2007 12:34:26 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Chris Mason <chris.mason@...cle.com>
CC:	Neil Brown <neilb@...e.de>, Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [patch 1/3] add the fsblock layer

Chris Mason wrote:
> On Mon, Jun 25, 2007 at 05:41:58PM +1000, Nick Piggin wrote:
> 
>>Neil Brown wrote:

>>>Why do you think you need PG_blocks?
>>
>>Block device pagecache (buffer cache) has to be able to accept
>>attachment of either buffers or blocks for filesystem metadata,
>>and call into either buffer.c or fsblock.c based on that.
>>
>>If the page flag is really important, we can do some awful hack
>>like assuming the first long of the private data is flags, and
>>those flags will tell us whether the structure is a buffer_head
>>or fsblock ;) But for now it is just easier to use a page flag.
> 
> 
> The block device pagecache isn't special, and certainly isn't that much
> code.  I would suggest keeping it buffer head specific and making a
> second variant that does only fsblocks.  This is mostly to keep the
> semantics of PagePrivate sane, lets not fuzz the line.

That would require a new inode and address_space for the fsblock
type blockdev pagecache, wouldn't it? I just can't think of a
better non-intrusive way of allowing a buffer_head filesystem and
an fsblock filesystem to live on the same blkdev together.

-- 
SUSE Labs, Novell Inc.
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