On Wed, May 01, 2013 at 11:20:44AM -0500, Ben Myers wrote: > Hi James, > > On Wed, May 01, 2013 at 01:39:09PM +0100, James Dingwall wrote: > > In reference to: http://oss.sgi.com/archives/xfs/2012-05/msg00046.html > > > > $ grep -r cleancache fs/xfs > > on the 3.9 kernel source suggests that no patch was submitted to > > enable cleancache for the XFS filesystem. Since it was suggested > > that this could be a one liner I've had a go and my first effort is > > inline below. While this seems to compile OK I have no experience > > in filesystems so I would appreciate it if anyone can point out that > > it is obviously wrong and likely to eat my data before I try booting > > the kernel. > > > > If it seems a reasonable attempt what would be the best way to check > > that it isn't doing nasty things? > > Hrm.. Looks like there is a doc in Documentation/vm/cleancache.txt which > includes a list of attributes the filesystem needs to have to work properly > with cleancache. So, those points are: | Some points for a filesystem to consider: | | - The FS should be block-device-based (e.g. a ram-based FS such | as tmpfs should not enable cleancache) OK. |- To ensure coherency/correctness, the FS must ensure that all | file removal or truncation operations either go through VFS or | add hooks to do the equivalent cleancache "invalidate" operations There be dragons - do all the XFS ioctls do the right thing? |- To ensure coherency/correctness, either inode numbers must | be unique across the lifetime of the on-disk file OR the | FS must provide an "encode_fh" function. Ok. |- The FS must call the VFS superblock alloc and deactivate routines | or add hooks to do the equivalent cleancache calls done there. OK. |- To maximize performance, all pages fetched from the FS should | go through the do_mpag_readpage routine or the FS should add | hooks to do the equivalent (cf. btrfs) xfs uses mpage_readpages() so should be fine. |- Currently, the FS blocksize must be the same as PAGESIZE. This | is not an architectural restriction, but no backends currently | support anything different. Which means that we need hooks in the mount path to determine if this is the case or not. I note that neither ext3/ext4 do this check so I can't determine why this restriction is mentioned, and I'm not sure if it has any relevance to btrfs. IOWs, I'd like to know why this restriction exists - what does cleancache care about how the filesystem maps blocks to the page in the page cache - any way the filesystem does this it uses page->private to hide this fact from the page cache.... |- A clustered FS should invoke the "shared_init_fs" cleancache | hook to get best performance for some backends. Not a problem. So there's a couple of things that need to be explained and explored, and a bunch of testing to be done.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
