On Wed, Sep 02, 2015 at 05:52:01PM +0100, Mel Gorman wrote: > On Mon, Aug 31, 2015 at 02:37:38PM -0700, Linus Torvalds wrote: > > On Sun, Aug 30, 2015 at 11:19 PM, Jan Kara <jack@xxxxxxx> wrote: > > > > > > The biggest change in the pull is the removal of ext3 filesystem driver > > > (~28k lines removed). > > > > I really am not ready to just remove ext3 without a lot of good > > arguments. There might well be people who this use ext3 as ext3, and > > don't want to update. I want more a rationale for removal than "ext4 > > can read old ext3 filesystems". > > > > This is not my area at all but as Jan said he was out on vacation and > offline so there is no chance for him to adjust the tree before the window > closes. I'm going going to try and guess what justifications he might have > used if he was online. > > 1. Backwards compatibility -- other knowledgeable people, particularly > Ted, already pointed out that backwards compatibility is guaranteed. > I know SLE is using the ext4 driver for ext3 filesystems and AFAIK, > there has been no bugs related to distro upgrades that failed to mount > an ext3 filesystem with the ext4 driver. As other distributions made > a similar decision and there is a lack of bug reports, there is some > evidence that the guarantee is adhered to > > > 2. ext4 driver performance -- when SLE considered switching to the ext4 > driver, I successfully checked that the ext4 driver matched or exceeded > the performance of the ext3 driver. Granted, this was limited in terms > of types of storage but as other distros are also using ext4 driver, > I'm guessing that no one found regressions. I don't have the data any > more but I don't recall a single instance where the ext3 driver was better > > 2. ext3-specific hack removals in block and VM. The merge request stated > that some workarounds in the VM and block layer could be got rid of but > I don't have a comprehensive list. Glancing at the branch though, at > least one hack is removed with "block: Remove forced page bouncing under I would be happy if the fs bounce buffering band-aid went away forever. :) > IO". I did not investigate deeply but it looks like cancel_dirty_page > is another potential candidate for going away. > > 3. Missing fixes. Fixes applied to ext4 have to be manually back-ported > to ext3, mostly by Jan, but it's possible one will be missed and ext3 > slowly bit rots. Ted already said this a lot better than I did so I'll > just repeat it > > Both Red Hat and SuSE, as well as Debian and Ubuntu, are using > ext4 with CONFIG_EXT4_USE_FOR_EXT23 for a couple of years now > to support ext2 and ext3 file systems. So with the exception of > some really ancient enterprise Linux distros, and people who are > manually configuring their systems, very few people are likely using > ext3 code base, which means the chances that it bitrots increases. > Basically, it's only been Jan's tireless work that has kept that > from happening, given that all of the major distro's have been > using ext4 to support ext2 and ext3 file systems. > > On the flip side, there does not appear to be any good reason for > keeping the ext3 driver around because if there ever is a case where an > old kernel is required to mount an ext3 filesystem then it appears the > ext4 developers would consider it a bug. Yes, that would be a bug. --D > > -- > Mel Gorman > SUSE Labs > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
