<snip> >> >> I again wonder if the ext4_defrag logic uses it? If so, HSM could >> leverage their design and basically piggy back on top of it. But only >> for a ext4 implementation. >> > Makes sense. > Yes, We have started analysis this. We will update you on this too. > I think, it should be helpful for us. My 2.6.28 kernel does not have ext4 defrag in it. I found it posted to the ext4 mailing list at the end of Sept. http://kerneltrap.org/mailarchive/linux-ext4/2008/9/27/3427244 The first patch in the series has the entry point ext4_defrag() in it. They invoke ext4_defrag() via ioctl. https://kerneltrap.org/mailarchive/linux-fsdevel/2008/9/27/3427104 Per the comments each call to ext4_defrag() defrags 64MB of data by allocating a 64MB contiguous group of blocks to a temporary inode and copying the data from the original into the new data blocks, then swapping just those blocks back into the original inode's block list. ext4_defrag() is holding the inodes mutex (lock) for the entire 64MB copy. I gather that the ioctl call returns to user space after each 64MB is defraged. Looks like there are some refinements to what has been discussed for OpenHSM, but nothing overly significant. In a very real way it seems to me that the ext4_defrag() should be generalized to allow multiple block allocation algorithms to be implemented. The rest of the code is likely identical between what ext4_defrag() needs and what OpenHSM needs. It might warrant ext4_defrag() being renamed to something like ext4_file_reorg() and then pass in the type of block allocation strategy to invoke. I suggest someone on the OHSM team should post a reply to the ext4 Sept. post and just let the ext4 team know a little of what you are working on. I doubt they will modify the patch at this point, but it is a good idea to let them know that their architecture can be put to broader use than they may be thinking. At a minimum the ABI for the ioctl should be flexible enough to allow OHSM to use the same ioctl and not cause the ext4 userland tools to have to change. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
