On Mon, Mar 19, 2007 at 11:06:33PM +0200, Artem Bityutskiy wrote: > On Mon, 2007-03-19 at 14:54 -0500, Matt Mackall wrote: > > The issue is 14000 lines of patch to make a parallel subsystem. > > Parallel system exists since very long. One is > flash->SW_or_HW_FTL->all_blkdev_stuff. The other is MTD->JFFS2. Think > about _why_ there are 2 of them. Hint - reliability, performance. Your > ranting basically says that only the first one makes sense. This is not > true.
A better way would be for MTD to deliver a block dev with a rich enough interface for JFFS2 to use efficiently in the first place. Yes, I know that can't be done with the current block dev layer. But that's what the source is for. > We enhance the second branch, not the first, please, realize this. Both > branches have their user base, and have always had. > > > iSCSI/nbd(6) > > | > > filesystem { swap | ext3 ext3 jffs2 > > \ | | | / > > / \ | dm-crypt->snapshot(5) / > > device mapper -| \ \ | / > > | partitioning / > > | | partitioning(4) > > | wear leveling(3) / > > | | / > > | block concatenation > > | | | | | > > \ bad block remapping(2) > > | | | | > > MTD raw block { raw block devices with no smarts(1) > > / | \ \ > > hardware { NAND NAND NAND NAND > > Matt, as I pointed in the first mail, flash != block device. And as I pointed out, you're wrong. It is both block oriented (eraseBLOCK??) and random access. That's what a block device is. The fact that it doesn't look like the other things that Linux currently calls a block device and supports well is another matter. > In your picture I see NAND->MTD raw block. So am I right that you > assume that we already have a decent FTL? The fact is that we do > not. No. Look at the picture for more than two seconds, please. I can tell you didn't do this because you didn't manage to find (1) which explicitly says "with no smarts". And you also cut out the footnote where I explained what I meant by "with no smarts". Find the spots marked (2) and (3). These are your FTL. > Please, bear in mind that decent FTL is difficult and an FS on top of > FTL is slow, FTL hits performance considerably. ...and if you'd actually looked at the picture, you'd have seen JFFS2 bypassing it. Along with another footnote explaining it. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/