ext4: speed up truncate/unlink by not using bforget() unless needed
authorAndrey Sidorov <qrxd43@motorola.com>
Wed, 19 Sep 2012 18:14:53 +0000 (14:14 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Wed, 19 Sep 2012 18:14:53 +0000 (14:14 -0400)
commit18888cf0883c286f238d44ee565530fe82752f06
treeebdc31cf2f7589b07bea8398cfb2d812f1a179c3
parent59e31c156a24d483bbd2ea07d4dc96043a55b6bc
ext4: speed up truncate/unlink by not using bforget() unless needed

Do not iterate over data blocks scanning for bh's to forget as they're
never exist. This improves time taken by unlink / truncate syscall.
Tested by continuously truncating file that is being written by dd.
Another test is rm -rf of linux tree while tar unpacks it. With
ordered data mode condition unlikely(!tbh) was always met in
ext4_free_blocks. With journal data mode tbh was found only few times,
so optimisation is also possible.

Unlinking fallocated 60G file after doing sync && echo 3 >
/proc/sys/vm/drop_caches && time rm --help

X86 before (linux 3.6-rc4):
# time rm -f test1
real    0m2.710s
user    0m0.000s
sys     0m1.530s

X86 after:
# time rm -f test1
real    0m0.644s
user    0m0.003s
sys     0m0.060s

MIPS before (linux 2.6.37):
# time rm -f test1
real    0m 4.93s
user    0m 0.00s
sys     0m 4.61s

MIPS after:
# time rm -f test1
real    0m 0.16s
user    0m 0.00s
sys     0m 0.06s

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrey Sidorov <qrxd43@motorola.com>
fs/ext4/extents.c