[Simh] Two questions

[Toby Thain]

On 12-Jul-06, at 12:20 PM, Tim Riker wrote:

> Gregg C Levine wrote:
>> Hello!
>> First Question:
>> I have TMPFS configured and probably working on my freshly  
>> activated and
>> running Linux system. SimH is also setup to run there. Now the  
>> question: How
>> would I go about informing the PDP-11 or VAX simulator that there  
>> is a
>> location on my physical system called <name> and that it uses  
>> TMPFS and that
>> it can use it as a virtual disk image up to about 10M. (Meg)
>
> Most Linux distros mount tmpfs on /dev/shm and allow all users write
> access with the sticky bit set like /tmp. tmpfs is is primarily ram
> based but will swap pages to disk like process memory.
>
> The kernel by default sets the max size of tmpfs to half of ram.  
> This is
> very conservative. I often set the size up to all of RAM plus all of
> swap as tmpfs will swap to disk. Now that's a bit aggresive on the  
> other
> end as you'll be in trouble if you really fill that up. You won't have
> any space left for processes. :)
>
> A better size choice would be someplace in the middle, perhaps half or
> ram plus half of swap?

It would depend on the real usage pattern of /tmp, would it not?

Without more detailed knowledge on what might fill /tmp on your  
system, on most systems half of RAM seems a useful safe default.

--T

> I would just change the size of /dev/shm and NOT
> mount another tmpfs mount someplace else. Something like:
>
> mount -o remount,size=3G /dev/shm
>
> Many distros have boot settings someplace to change this. For Debian
> it's the setting SHM_SIZE in /etc/default/tmpfs, for SuSE it's
> SHMFS_SIZE in /etc/sysconfig/kernel for example.
>
> I'm not sure how you would tell simh pdp-11 about it. You could copy
> disk images over there and then tell simh to use those, but then you
> need to be sure to copy any disk images back that you wish to preserve
> changes as the tmpfs files disappear on the next reboot.
>
> I'll leave the other ?s to those with more pdp-11 knowledge.
> -- 
> Tim Riker - http://Rikers.org/ - TimR at Debian.org
> Embedded Linux Technologist - http://eLinux.org/
> BZFlag maintainer - http://BZFlag.org/ - for fun!
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