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Re: [Xen-users] crazy SWAP and RAM idea

To: SH Solutions <info@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] crazy SWAP and RAM idea
From: Tim Post <tim.post@xxxxxxxxxxxxxxx>
Date: Fri, 08 Sep 2006 22:22:39 +0800
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Crazy is a good word for it .. but would be interesting to see the

I'd use a CF or USB stick (as large as you can find) to do that with,
sounds rather adventurous, but I think would prove to be problematic.

Kernel frees swap very quickly after it becomes available, so your
basically preventing all services on the dom-u's from caching idle
children, and they'd need to fork for every connection. It would be a
significant performance degradation. 

If you used conventional ramdisks, you'd be able to fry an egg on the

Good luck however :) 


On Thu, 2006-09-07 at 23:26 +0200, SH Solutions wrote:
> Hi
> I've been thinking about the following:
> As every domU has it's own RAM, I cannot give as much memory to each domU,
> as I wanted to.
> So I gave them swap. That's LVM-backed.
> But now, each domain that exceeds it's memory needs to swap pages in and
> out, while other domains might not need their memory.
> The idea to solve this, is a follows:
> 1. Give every domU as few memory as possible. (16MB?)
> 2. Give dom0 a huge fast swap space (several GB?)
> 3. Create a "RAMDRIVE" in dom0 in that swap.
> 4. Create domU's swap partitions on dom0's ramdrive.
> The reason would be that dom0 can now "really" swap in pages as *REALLY*
> needed from/to harddrive.
> DomU's would then "only" swap from/to a partition that really is RAM and as
> such really fast.
> Seems a little crazy idea, but a way to make swaping more sensfull.
> What do you think?
> Regards,
>   Steffen
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