Hi everyone, This fourth patchriver has two faces -- one way of looking at it is that it is random odds and ends at the tail of my development tree. A second interpretation is that it is necessary pieces for defragmenting free space, which is a precursor for online shrink of XFS filesystems. The kernel side isn't that exciting -- we export refcounting information for space extents, and add a new fallocate mode for mapping exact portions of free filesystem space into a file. Userspace is where things get interesting! The free space defragmenter is an iterative algorithm that assigns free space to a dummy file, and then uses the GETFSMAP and GETFSREFCOUNTS information to target file space extents in order of decreasing share counts. Once an extent has been targeted, it uses reflinking to freeze the space, copies it elsewhere, and uses FIDEDUPERANGE to remap existing file data until the dummy file is the sole owner of the targetted space. If metadata are involved, the defrag utility invokes online repair to rebuild the metadata somewhere else. Since last year, I've also merged in Dave's xfs_spaceman code to move inodes. I've not had much time to play with it otherwise. When the defragmenter finishes, all the free space has been isolated to the dummy file, which can be unlinked and closed if defragmentation was the goal; or it could be passed to a shrinkfs operation. --D
