Hi Omar,
Thanks for your patchset.
Quite a nice one, and debug-tree can give better output on space cache.
With current implement, space cache is near a black box in debug-tree
output.
And current on disk format is not quite easy to understand.(In fact,
space cache is restored in tree root, as a NODATACOW inode, quite wired)
Also, it should provide a quite good base for rework inode cache for
future development.
But I'm still a little concerned about the performance.
One of the problem using b-tree is, now we need to use
btrfs_search_slot() to do modification, that means we will do
level-based tree lock and COW.
Personally speaking, I'd like to blame that for the slow metadata
performance of btrfs.
(Yeah personal experience, may be wrong again)
So with the new implement every space cache operation will causing tree
lock and cow.
Unlike the old wired structure, which is done in a NODATACOW fashion.
Hopes I'm wrong about it (and it seems I'm always wrong about all these
assumption based performance thing).
Thanks,
Qu
Omar Sandoval wrote on 2015/09/03 12:44 -0700:
Here's version 2 of the the free space B-tree patches, addressing
Josef's review from the last round, which you can find here:
http://www.spinics.net/lists/linux-btrfs/msg46713.html
Changes from v1->v2:
- Cleaned up a bunch of unnecessary instances of "if (ret) goto out; ret = 0"
- Added aborts in the free space tree code closer to the site the error
is encountered: where we add or remove block groups, add or remove
free space, and also when we convert formats
- Moved loading of the free space tree into caching_thread() and added a
new patch 4 in preparation for it
- Commented a bunch of stuff in the extent buffer bitmap operations and
refactored some of the complicated logic
- Added sanity tests for the extent buffer bitmap operations and free
space tree (patches 2 and 6)
- Added Josef's Reviewed-by tags
Omar Sandoval (9):
Btrfs: add extent buffer bitmap operations
Btrfs: add extent buffer bitmap sanity tests
Btrfs: add helpers for read-only compat bits
Btrfs: refactor caching_thread()
Btrfs: introduce the free space B-tree on-disk format
Btrfs: implement the free space B-tree
Btrfs: add free space tree sanity tests
Btrfs: wire up the free space tree to the extent tree
Btrfs: add free space tree mount option
fs/btrfs/Makefile | 5 +-
fs/btrfs/ctree.h | 107 ++-
fs/btrfs/disk-io.c | 26 +
fs/btrfs/extent-tree.c | 112 ++-
fs/btrfs/extent_io.c | 183 +++-
fs/btrfs/extent_io.h | 10 +-
fs/btrfs/free-space-tree.c | 1501 ++++++++++++++++++++++++++++++++
fs/btrfs/free-space-tree.h | 71 ++
fs/btrfs/super.c | 24 +-
fs/btrfs/tests/btrfs-tests.c | 52 ++
fs/btrfs/tests/btrfs-tests.h | 10 +
fs/btrfs/tests/extent-io-tests.c | 138 ++-
fs/btrfs/tests/free-space-tests.c | 35 +-
fs/btrfs/tests/free-space-tree-tests.c | 570 ++++++++++++
fs/btrfs/tests/qgroup-tests.c | 20 +-
include/trace/events/btrfs.h | 3 +-
16 files changed, 2763 insertions(+), 104 deletions(-)
create mode 100644 fs/btrfs/free-space-tree.c
create mode 100644 fs/btrfs/free-space-tree.h
create mode 100644 fs/btrfs/tests/free-space-tree-tests.c
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