[LTP] [PATCH] readahead02: estimate max readahead size

[Cyril Hrubis]

Hi!
> > I've tried this on the /tmp on Btrfs and got max_ra_estimage nearly ten times
> > greater than the sysfs value. But apart from that the measured times are
> > pretty
> > much comparable with the previous version, which suggests that maximal
> > readahead size on Btrfs is set to ~4M and the limit per device is not
> > applicable.
> > 
> > Did you get the estimate close to the value of the sysfs file in your
> > environment?
> 
> I do (on 4.8 x86 KVM guest):
> # cat /sys/devices/virtual/bdi/253:1/read_ahead_kb
> 4096
> readahead02    0  TINFO  :  max ra estimate: 4145152
> 
> Are you using upstream kernel or a patched one?

That is Btrfs on SLES12-SP2 RC with kernel 4.4.21, but it seems to be
pretty much Btrfs specific. If I point TMPDIR to ext3 fs I got estimated
ra 507904 while the read_ahead_kb for the device is set to 512.

-- 
Cyril Hrubis
chrubis@suse.cz