md /tmp and async mounts

[Robert Watson]

On Thu, 1 Jun 2006, Kris Kennaway wrote:

> On Fri, Jun 02, 2006 at 12:35:27AM +0300, Giorgos Keramidas wrote:
>
>>> I think it should be the default.  I think we should also avoid using -M 
>>> (malloc backing for md) in favour of swap backing because of the panic 
>>> problems - this is too easy to trigger by accident and it makes FreeBSD 
>>> look bad since it looks like a bug.
>>
>> Ok, I'll prepare a patch that enables async and disables -M.  We should 
>> also document the fact that tmpmfs="YES" and varmfs="YES" in rc.conf may 
>> require the presence of at least one swap device by default, and point the 
>> users to -M with a warning if they run FreeBSD without a swap device but 
>> still want to use tmpmfs or varmfs :)
>
> Actually I thought about this and don't think it's the case.  swap backing 
> doesn't use swap unless you have memory pressure, and if you have memory 
> pressure and no swap your system is going to explode regardless.

My feeling is that swap-backed md should have been the default years ago.  We 
could add a sanity test to mdconfig that generates a warning if swap-backed md 
is configured but swapping isn't configured.

Robert N M Watson