On Wed 04-10-17 10:41:51, Darrick J. Wong wrote: > On Wed, Oct 04, 2017 at 11:12:05AM +0200, Jan Kara wrote: > > Increase default maximum allowed readahead window from 128 KB to 512 KB. > > This improves performance for some workloads (see below for details) where > > ability to scale readahead window to larger sizes allows for better total > > throughput while chances for regression are rather low given readahead > > window size is dynamically computed based on observation (and thus it never > > grows large for workloads with a random read pattern). > > > > Note that the same tuning can be done using udev rules or by manually setting > > the sysctl parameter however we believe the new value is a better default most > > users will want to use. As a data point we carry this patch in SUSE kernels > > for over 8 years. > > > > Some data from the last evaluation of this patch (on 4.4-based kernel, I can > > rerun those tests on a newer kernel but nothing has changed in the readahead > > area since 4.4). The patch was evaluated on two machines > > This is purely speculating, but I think this is worth at least a quick > retry on 4.14 to see what's changed in the past 10 kernel release. For > one thing, ext3 no longer exists, and XFS' file IO path has changed > quite a lot since then. ext3 in this test is actually using ext4 driver already, so that has not changed. I agree XFS has changed quite a bit so results might differ there. I can rerun it with current kernel to see whether XFS behavior changed. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
