On Tue, Apr 11, 2017 at 03:54:18PM +0200, Jan Kara wrote: > Currently ext4_writepages() submits all pages with transaction started. > When no page needs block allocation or extent conversion we can submit > all dirty pages in the inode while holding a single transaction handle > and when device is congested this can take significant amount of time. > Thus ext4_writepages() can block transaction commits for extended > periods of time. > > Take for example a simple benchmark simulating PostgreSQL database > (pgioperf in mmtest). The benchmark runs 16 processes doing random reads > from a huge file, one process doing random writes to the huge file, and > one process doing sequential writes to a small writes and frequently > running fsync. With unpatched kernel transaction commits take on average > ~18s with standard deviation of ~41s, top 5 commit times are: > > 274.466639s, 126.467347s, 86.992429s, 34.351563s, 31.517653s. > > After this patch transaction commits take on average 0.1s with standard > deviation of 0.15s, top 5 commit times are: > > 0.563792s, 0.519980s, 0.509841s, 0.471700s, 0.469899s > > Signed-off-by: Jan Kara <jack@xxxxxxx> Great work! Many thanks. Apologies for the late application; April has been crazy busy. I'm kicking off a full regression test, but it looks good. - Ted
