mfs/mdconfig under RELENG_5: malloc vs swap-backed

[João Carlos Mendes Luis]

Bernd Walter wrote:
> On Fri, Jul 29, 2005 at 09:41:24PM +0400, Dmitry Morozovsky wrote:
> 
>>Dear colleagues,
>>
>>can anyone please point me why mdconfig method for tmpmfs  
>>is malloc-backed instead of swap-backed, and it is hardcoded into rc.subr? 
>>
>>Are swap-backed file systems so inefficient? If no, why not move -M to 
>>/etc/defaultc/rc.conf so admin can override this behaviour?
> 
> 
> Diskless systems may not have swap - the default is required as is.
> Don't know about beeing hardcoded.

It is hardcoded at /etc/rc.subr:

# Provide a function for normalizing the mounting of memory
# filesystems.  This should allow the rest of the code here to remain
# as close as possible between 5-current and 4-stable.
#   $1 = size
#   $2 = mount point
#   $3 = (optional) extra mdmfs flags
mount_md() {
         if [ -n "$3" ]; then
                 flags="$3"
         fi
         /sbin/mdmfs $flags -s $1 -M md $2
}

I would prefer it to be configurable, too.