From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <468082FF.6090704@yahoo.com.au> Date: Tue, 26 Jun 2007 13:07:43 +1000 From: Nick Piggin MIME-Version: 1.0 Subject: Re: [patch 1/3] add the fsblock layer References: <20070624014528.GA17609@wotan.suse.de> <20070624014613.GB17609@wotan.suse.de> <18046.63436.472085.535177@notabene.brown> <467F71C6.6040204@yahoo.com.au> <20070625122906.GB12446@think.oraclecorp.com> <46807B32.6050302@yahoo.com.au> <18048.32372.40011.10896@notabene.brown> In-Reply-To: <18048.32372.40011.10896@notabene.brown> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Neil Brown Cc: Chris Mason , Nick Piggin , Linux Kernel Mailing List , Linux Memory Management List , linux-fsdevel@vger.kernel.org List-ID: Neil Brown wrote: > On Tuesday June 26, nickpiggin@yahoo.com.au wrote: > >>Chris Mason wrote: >> >>>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. > > > I don't think they would ever try to. Both filesystems would bd_claim > the blkdev, and only one would win. Hmm OK, I might have confused myself thinking about partitions... > The issue is more of a filesystem sharing a blockdev with the > block-special device (i.e. open("/dev/sda1"), read) isn't it? > > If a filesystem wants to attach information to the blockdev pagecache > that is different to what blockdev want to attach, then I think "Yes" > - a new inode and address space is what it needs to create. > > Then you get into consistency issues between the metadata and direct > blockdevice access. Do we care about those? Yeah that issue is definitely a real one. The problem is not just consistency, but "how do the block device aops even know that the PG_private page they have has buffer heads or fsblocks", so it is an oopsable condition rather than just a plain consistency issue (consistency is already not guaranteed). -- SUSE Labs, Novell Inc. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org