Re: [Xen-users] Use of memory on Dom0 ?

["Olivier B." <xen.list@xxxxxxxxx>]

Fajar A. Nugraha a écrit :
> On Thu, Feb 11, 2010 at 11:35 PM, Olivier B. <xen.list@xxxxxxxxx> wrote:
>   
> > You're right, it's a solution yes (all my domU are PV).
> > But how does it works if a software use "1800" of that memory, and I reduce
> > it to 1000 ?
> >     
> It'd behave the same as if you run another software that uses 800M of
> memory. On most cases it'd just use swap. On some cases (like when the
> app specifically lock the memory it uses, making it unswappable) it
> might make domU crash or experience OOM.
>
>   
> > Or maybe is there a way to reserve this memory for disk caching only ?
> >     
> No direct way that I know of. You need to know how much memory your
> application needs/uses.
> Linux uses available memory for cache. If your application only use
> 1000M, then the rest (800M) will be used for caching. That 800M can be
> ballooned-down safely.
>
> If your application always need 1800M, then you should assign more
> memory from the start.
>
>   
Ok, the problem is that it's not "my application", it's users's 
applications, I don't really control what they do with their DomU.
If I use file backend for a partition, will it use the Dom0 memory for 
read cache ? (if Xen doesn't open files in O_DIRECT mode...)
In this case I can use 12Go to increase the DomU's memory by 50%, and 
12Go as read cache from dom0 for domu's swap files :D Maybe it's a bad 
idea ?
Olivier

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