Re: [dm-devel] [Lsf-pc] [LSF/MM TOPIC] a few storage topics

[Jeff Moyer <jmoyer redhat com>]

Chris Mason <chris mason oracle com> writes:

>> All three filesystems use the generic mpages code for reads, so they
>> all get the same (bad) I/O patterns.  Looks like we need to fix this up
>> ASAP.
>
> Can you easily run btrfs through the same rig?  We don't use mpages and
> I'm curious.

The readahead code was to blame, here.  I wonder if we can change the
logic there to not break larger I/Os down into smaller sized ones.
Fengguang, doing a dd if=file of=/dev/null bs=1M results in 128K I/Os,
when 128KB is the read_ahead_kb value.  Is there any heuristic you could
apply to not break larger I/Os up like this?  Does that make sense?

Cheers,
Jeff