I've been working to try to improve the write-ahead log's performance,
and I found that the bottleneck addresses in the checksum items,
especially when we want to make a random write on a large file, e.g a 4G file.
Then a idea for this suggested by Chris is to use sub transaction ids and just
to log the part of inode that had changed since either the last log commit or
the last transaction commit. And as we also push the sub transid into the btree
blocks, we'll get much faster tree walks. As a result, we abandon the original
brute force approach, which is "to delete all items of the inode in log",
to making sure we get the most uptodate copies of everything, and instead
we manage to "find and merge", i.e. finding extents in the log tree and merging
in the new extents from the file.
This patchset puts the above idea into code, and although the code is now more
complex, it brings us a great deal of performance improvement:
in my sysbench "write + fsync" test:
451.01Kb/sec -> 4.3621Mb/sec
In v2, thanks to Chris, we worked together to solve 2 bugs, and after that it
works as expected.
Since there are some vital changes in recent rc, like "kill trans_mutex" and
"use cur_trans", as David asked, I rebase the patchset to the latest for-linus
branch.
More tests are welcome!
You can also get this patchset from:
git://repo.or.cz/linux-btrfs-devel.git sub-trans
Liu Bo (12):
Btrfs: introduce sub transaction stuff
Btrfs: update block generation if should_cow_block fails
Btrfs: modify btrfs_drop_extents API
Btrfs: introduce first sub trans
Btrfs: still update inode trans stuff when size remains unchanged
Btrfs: improve log with sub transaction
Btrfs: add checksum check for log
Btrfs: fix a bug of log check
Btrfs: kick off useless code
Btrfs: deal with EEXIST after iput
Btrfs: use the right generation number to read log_root_tree
Revert "Btrfs: do not flush csum items of unchanged file data during
treelog"
fs/btrfs/btrfs_inode.h | 12 ++-
fs/btrfs/ctree.c | 69 +++++++++---
fs/btrfs/ctree.h | 5 +-
fs/btrfs/disk-io.c | 12 +-
fs/btrfs/extent-tree.c | 10 +-
fs/btrfs/file.c | 22 ++---
fs/btrfs/inode.c | 33 ++++---
fs/btrfs/ioctl.c | 6 +-
fs/btrfs/relocation.c | 6 +-
fs/btrfs/transaction.c | 14 ++-
fs/btrfs/transaction.h | 19 +++-
fs/btrfs/tree-defrag.c | 2 +-
fs/btrfs/tree-log.c | 272 ++++++++++++++++++++++++++++++++++-------------
13 files changed, 331 insertions(+), 151 deletions(-)
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