From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from majordomo by infradead.org with local (Exim 3.03 #1) id 1398jH-0004AN-00 for mtd-list@infradead.org; Mon, 03 Jul 2000 17:05:52 +0100 Received: from dns.cygnus.co.uk ([194.130.39.3] helo=pasanda.cygnus.co.uk) by infradead.org with smtp (Exim 3.03 #1) id 1398jG-0004AG-00 for mtd@infradead.org; Mon, 03 Jul 2000 17:05:50 +0100 From: David Woodhouse In-Reply-To: References: To: Alan Cox Cc: nico@cam.org (Nicolas Pitre), jgg@ualberta.ca (Jason Gunthorpe), bjorn.wesen@axis.com (Bjorn Wesen), jffs-dev@axis.com, mtd@infradead.org Subject: Re: garbage collect Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Mon, 03 Jul 2000 17:09:38 +0100 Message-ID: <21897.962640578@cygnus.co.uk> Sender: owner-mtd@infradead.org List-ID: alan@lxorguk.ukuu.org.uk said: > The interesting question is should they. I don't (currently) think so. It's fairly difficult to fit flash into the block device model. JFFS is the primary user of MTD devices now - everything else (i.e. FTL, NFTL) is a second class citizen. JFFS writes variable-size nodes, and doing that on a block device would mean wasting RAM on grouping writes into blocksized chunks. And what do you set your blocksize to? On most NOR flash devices, it's something like 128Kb. We need to support sub-blocksize writes, and we need that to be explicitly controlled by the user, so it can optimally balance the journalling requirements with the desire to have as few write cycles as possible. > Withouth them going via the block layer you wont be able to mirror > them Mirrored flash? That's just sick. And anyway, it needs to be done at a higher level than the individual flash chips - on which you may have bad blocks in different places, which need to be mapped round differently on each chip. Currently, if you want mirrored flash, you have to use {N,}FTL to provide emulated block devices on top of which you stick your RAID array. It's feasible to add direct mirroring support to JFFS, though, if it's really a necessary feature. > or potentially run a loopback fs over them soon That's even sicker, and should arguably be done in userspace with nbd. -- dwmw2 To unsubscribe, send "unsubscribe mtd" to majordomo@infradead.org