1. 03 4月, 2009 1 次提交
  2. 25 3月, 2009 4 次提交
    • C
      Btrfs: make sure btrfs_update_delayed_ref doesn't increase ref_mod · 1a81af4d
      Chris Mason 提交于
      btrfs_update_delayed_ref is optimized to add and remove different
      references in one pass through the delayed ref tree.  It is a zero
      sum on the total number of refs on a given extent.
      
      But, the code was recording an extra ref in the head node.  This
      never made it down to the disk but was used when deciding if it was
      safe to free the extent while dropping snapshots.
      
      The fix used here is to make sure the ref_mod count is unchanged
      on the head ref when btrfs_update_delayed_ref is called.
      Signed-off-by: NChris Mason <chris.mason@oracle.com>
      1a81af4d
    • C
      Btrfs: process the delayed reference queue in clusters · c3e69d58
      Chris Mason 提交于
      The delayed reference queue maintains pending operations that need to
      be done to the extent allocation tree.  These are processed by
      finding records in the tree that are not currently being processed one at
      a time.
      
      This is slow because it uses lots of time searching through the rbtree
      and because it creates lock contention on the extent allocation tree
      when lots of different procs are running delayed refs at the same time.
      
      This commit changes things to grab a cluster of refs for processing,
      using a cursor into the rbtree as the starting point of the next search.
      This way we walk smoothly through the rbtree.
      Signed-off-by: NChris Mason <chris.mason@oracle.com>
      c3e69d58
    • C
      Btrfs: try to cleanup delayed refs while freeing extents · 1887be66
      Chris Mason 提交于
      When extents are freed, it is likely that we've removed the last
      delayed reference update for the extent.  This checks the delayed
      ref tree when things are freed, and if no ref updates area left it
      immediately processes the delayed ref.
      Signed-off-by: NChris Mason <chris.mason@oracle.com>
      1887be66
    • C
      Btrfs: do extent allocation and reference count updates in the background · 56bec294
      Chris Mason 提交于
      The extent allocation tree maintains a reference count and full
      back reference information for every extent allocated in the
      filesystem.  For subvolume and snapshot trees, every time
      a block goes through COW, the new copy of the block adds a reference
      on every block it points to.
      
      If a btree node points to 150 leaves, then the COW code needs to go
      and add backrefs on 150 different extents, which might be spread all
      over the extent allocation tree.
      
      These updates currently happen during btrfs_cow_block, and most COWs
      happen during btrfs_search_slot.  btrfs_search_slot has locks held
      on both the parent and the node we are COWing, and so we really want
      to avoid IO during the COW if we can.
      
      This commit adds an rbtree of pending reference count updates and extent
      allocations.  The tree is ordered by byte number of the extent and byte number
      of the parent for the back reference.  The tree allows us to:
      
      1) Modify back references in something close to disk order, reducing seeks
      2) Significantly reduce the number of modifications made as block pointers
      are balanced around
      3) Do all of the extent insertion and back reference modifications outside
      of the performance critical btrfs_search_slot code.
      
      #3 has the added benefit of greatly reducing the btrfs stack footprint.
      The extent allocation tree modifications are done without the deep
      (and somewhat recursive) call chains used in the past.
      
      These delayed back reference updates must be done before the transaction
      commits, and so the rbtree is tied to the transaction.  Throttling is
      implemented to help keep the queue of backrefs at a reasonable size.
      
      Since there was a similar mechanism in place for the extent tree
      extents, that is removed and replaced by the delayed reference tree.
      
      Yan Zheng <yan.zheng@oracle.com> helped review and fixup this code.
      Signed-off-by: NChris Mason <chris.mason@oracle.com>
      56bec294