• Liu Bo's avatar
    Btrfs: improve fsync by filtering extents that we want · 4e2f84e6
    Liu Bo authored
    This is based on Josef's "Btrfs: turbo charge fsync".
    
    The above Josef's patch performs very good in random sync write test,
    because we won't have too much extents to merge.
    
    However, it does not performs good on the test:
    dd if=/dev/zero of=foobar bs=4k count=12500 oflag=sync
    
    The reason is when we do sequencial sync write, we need to merge the
    current extent just with the previous one, so that we can get accumulated
    extents to log:
    
    A(4k) --> AA(8k) --> AAA(12k) --> AAAA(16k) ...
    
    So we'll have to flush more and more checksum into log tree, which is the
    bottleneck according to my tests.
    
    But we can avoid this by telling fsync the real extents that are needed
    to be logged.
    
    With this, I did the above dd sync write test (size=50m),
    
             w/o (orig)   w/ (josef's)   w/ (this)
    SATA      104KB/s       109KB/s       121KB/s
    ramdisk   1.5MB/s       1.5MB/s       10.7MB/s (613%)
    Signed-off-by: default avatarLiu Bo <bo.li.liu@oracle.com>
    4e2f84e6
inode.c 207 KB