Time to increase MAXPHYS?

[Julian Elischer]

On 4/6/17 4:59 am, Colin Percival wrote:
> On January 24, 1998, in what was later renumbered to SVN r32724, dyson@
> wrote:
>> Add better support for larger I/O clusters, including larger physical
>> I/O.  The support is not mature yet, and some of the underlying implementation
>> needs help.  However, support does exist for IDE devices now.
> and increased MAXPHYS from 64 kB to 128 kB.  Is it time to increase it again,
> or do we need to wait at least two decades between changes?
>
> This is hurting performance on some systems; in particular, EC2 "io1" disks
> are optimized for 256 kB I/Os, EC2 "st1" (throughput optimized spinning rust)
> disks are optimized for 1 MB I/Os, and Amazon's NFS service (EFS) recommends
> using a maximum I/O size of 1 MB (and despite NFS not being *physical* I/O it
> seems to still be limited by MAXPHYS).
>
We increase it in freebsd 8 and 10.3 on our systems,  Only good results.

sys/sys/param.h:#define MAXPHYS         (1024 * 1024)   /* max raw I/O 
transfer size */