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Date: Mon, 14 Jun 2010 10:46:42 -0400 From: Ric Wheeler <rwheeler@...hat.com> To: "Theodore Ts'o" <tytso@....edu> CC: linux-ext4@...r.kernel.org Subject: Re: E2fsprogs master branch now has all 64-bit patch applied On 06/14/2010 09:39 AM, Theodore Ts'o wrote: > It's taken way too long, but I've finally finished integrating the > 64-bit patches into e2fsprogs's mainline repository. All of the > necessary patches should now be in the master branch for e2fsprogs. > > The big change from before is that I replaced Val's changes for fixing > up how mke2fs picked the correct fs-type profile from mke2fs.conf with > something that I think works much better and leaves the code much > cleaner. With this change you need to add the following to your > /etc/mke2fs.conf file if you want to enable the 64-bit feature flag > automatically for a big disk: > > [fs_types] > ext4 = { > features = has_journal,extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize > auto_64-bit_support = 1 #<---- add this line > inode_size = 256 > } > > Alternatively you can change the features line to include the feature > "64bit"; this will force the use of the 64-bit fields, and double the > size of the block group descriptors, even for smaller file systems that > don't require the 64-bit support. (This was one of my problems with > Val's implementation; it forced the mke2fs.conf file to always enable > the 64-bit feature flag, which would cause backwards compatibility > issues.) This might be a good thing to do for debugging purposes, > though, so this is an option which I left open, but the better way of > doing things is to use the auto_64-bit-support flag. > > Should the default for auto_64-bit-support be on or off? For now I've > left it to be defaulted to "off", on the theory that it might be useful > for distributions that aren't quite ready to enable 64-bit support until > we do a lot more testing. But I may very well change this default > before 1.42 ships, on the theory that people who want to disable this > just ship an edited mke2fs.conf file. (Users can always explicit > request 64bit support by using "mke2fs -O 64bit", of course.) Comments > on this would be appreciated. > > The other support which I've added into mke2fs.conf handling is I've > added two additional automatically selected fs-types, which work like > "floppy" and "small". These are "big" which is automatically selected > for filesystems>= 4TB, and and "huge" which is elected for filesystems > >> = 16TB. I'm not 100% sure this will be useful, but it seemed like >> > it might be useful to have these. Again, comments appreciated it; the > names and the cutoff points may change before the 1.42 release. > > What are things that are still left to be done before we 64-bit support > is completely supported? Just a few things: > > * Currently the badblocks list mechanism only supports 32-bit blocks. > This may be OK, since running "badblocks" on a really large disk is > probably a fool's errand. But how we handle this is an open question; > should we just refuse "mke2fs -c" or "e2fsck -c" for really big file > systems? Should we deprecate the badblocks inode altogether? > I think that badblocks is pretty much a legacy item at this point. Certainly not common on really large devices which are almost always RAID'ed in some form. Thanks! Ric > * The online resizing code, which relies on using a resize inode and > indirect blocks, will not scale to 64-bit filesystems. We have the > beginnings of support for the "meta_bg" style of resizing, which is > supported by the kernel and the e2fsprogs code --- but it hasn't been > implemented in the kernel yet. We need to add that. > > As a related note, currently the online resizing code doesn't > understand about flex_bg, so the filesystem layout for filesystems > which are grown using online resizing is definitely not optimized for > flex_bg. This is something that we would probably want to fix at the > same time, since it means adding a new ioctl interface between the > kernel and the resize2fs program. > > - Ted > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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