BSD 4.2 minphys() < 64K

[Jim Franklin]

Why does minphys() in BSD 4.2 systems still limit block i/o transfers to
63 * 1024 bytes?  I assume that this is an ancient artifact from PDP-11
days, when int's were 16 bits and 64K bytes was considered a lot of
memory.

But processor memory is very cheap now, so we can afford to allocate much
larger buffer pools.  Block devices such as disks are also much faster
and have higher densities. For example, 64K bytes is only 2 tracks on a
Fujitsu 2361.  I would like to be able to blast a 1/4 megabyte to a disk in
one i/o -- the disk, disk controller, and device driver can all deal with
this.  But minphys() is the bottleneck.

Does anyone know why minphys is still < 64 K?  Has anyone successfully
increased this, or know why it can't be done?  Thanks ...
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{harvard!adelie,{decvax,allegra,talcott}!encore}!munsell!jwf

Jim Franklin, Eikonix Corp., 23 Crosby Drive, Bedford, MA 01730
Phone: (617) 275-5070 x415