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  1. 24 Mar, 2009 5 commits
    • Chris Mason's avatar
      Btrfs: process the delayed reference queue in clusters · c3e69d58
      Chris Mason authored 
      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: default avatarChris Mason <chris.mason@oracle.com>
      c3e69d58
    • Chris Mason's avatar
      Btrfs: try to cleanup delayed refs while freeing extents · 1887be66
      Chris Mason authored 
      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: default avatarChris Mason <chris.mason@oracle.com>
      1887be66
    • Chris Mason's avatar
      Btrfs: reduce stack usage in some crucial tree balancing functions · 44871b1b
      Chris Mason authored 
      Many of the tree balancing functions follow the same pattern.

1) cow a block
2) do something to the result

This commit breaks them up into two functions so the variables and
code required for part two don't suck down stack during part one.
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
      44871b1b
    • Chris Mason's avatar
      Btrfs: do extent allocation and reference count updates in the background · 56bec294
      Chris Mason authored 
      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: default avatarChris Mason <chris.mason@oracle.com>
      56bec294
    • Chris Mason's avatar
      Btrfs: don't preallocate metadata blocks during btrfs_search_slot · 9fa8cfe7
      Chris Mason authored 
      In order to avoid doing expensive extent management with tree locks held,
btrfs_search_slot will preallocate tree blocks for use by COW without
any tree locks held.

A later commit moves all of the extent allocation work for COW into
a delayed update mechanism, and this preallocation will no longer be
required.
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
      9fa8cfe7
  3. 23 Mar, 2009 11 commits
  5. 22 Mar, 2009 6 commits
  7. 21 Mar, 2009 2 commits
  9. 20 Mar, 2009 5 commits
  11. 19 Mar, 2009 11 commits
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