When we recover from crash via write-ahead log tree and process
the inode refs, for each btrfs_inode_ref item, we will
1) check if we already have a perfect match in fs/file tree, if
we have, then we're done.
2) search the corresponding back reference in fs/file tree, and
check all the names in this back reference to see if they are
also in the log to avoid conflict corners.
3) recover the logged inode refs to fs/file tree.
In current btrfs, however,
- for 2)'s check, once is enough, since the checked back reference
will remain unchanged after processing all the inode refs belonged
to the key.
- it has no need to do another 1) between 2) and 3).
I've made a small test to show how it improves,
$dd if=/dev/zero of=foobar bs=4K count=1
$sync
$make 100 hard links continuously, like ln foobar link_i
$fsync foobar
$echo b > /proc/sysrq-trigger
after reboot
$time mount DEV PATH
without patch:
real 0m0.285s
user 0m0.001s
sys 0m0.009s
with patch:
real 0m0.123s
user 0m0.000s
sys 0m0.010s
Changelog v1->v2:
- fix double free - pointed by David Sterba
Changelog v2->v3:
- adjust free order
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
c622ae6085