• Qu Wenruo's avatar
    btrfs: qgroup: Use generation-aware subtree swap to mark dirty extents · 5f527822
    Qu Wenruo authored
    Before this patch, with quota enabled during balance, we need to mark
    the whole subtree dirty for quota.
    OO = Old tree blocks (from file tree)
    NN = New tree blocks (from reloc tree)
            File tree (src)		          Reloc tree (dst)
                OO (a)                              NN (a)
               /  \                                /  \
         (b) OO    OO (c)                    (b) NN    NN (c)
            /  \  /  \                          /  \  /  \
           OO  OO OO OO (d)                    OO  OO OO NN (d)
    For old balance + quota case, quota will mark the whole src and dst tree
    dirty, including all the 3 old tree blocks in reloc tree.
    It's doable for small file tree or new tree blocks are all located at
    lower level.
    But for large file tree or new tree blocks are all located at higher
    level, this will lead to mark the whole tree dirty, and be unbelievably
    This patch will change how we handle such balance with quota enabled
    Now we will search from (b) and (c) for any new tree blocks whose
    generation is equal to @last_snapshot, and only mark them dirty.
    In above case, we only need to trace tree blocks NN(b), NN(c) and NN(d).
    (NN(a) will be traced when COW happens for nodeptr modification).  And
    also for tree blocks OO(b), OO(c), OO(d). (OO(a) will be traced when COW
    happens for nodeptr modification.)
    For above case, we could skip 3 tree blocks, but for larger tree, we can
    skip tons of unmodified tree blocks, and hugely speed up balance.
    This patch will introduce a new function,
    btrfs_qgroup_trace_subtree_swap(), which will do the following main
    1) Read out real root eb
       And setup basic dst_path for later calls
    2) Call qgroup_trace_new_subtree_blocks()
       To trace all new tree blocks in reloc tree and their counter
       parts in the file tree.
    Signed-off-by: default avatarQu Wenruo <wqu@suse.com>
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>