Re: [Xen-devel] [PATCH] RFC: initial libxl support for xenpaging

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Fri, Feb 17, 2012 at 4:43 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:

> My point is that the memory knobs should be exposed to the user of xl as
> semantically meaningful options without the need to refer to "the paging
> target" or "the balloon target" which is why there should not IMHO be
> "xl commands to adjust just ballooning and/or paging".

I disagree with this.  I agree completely that the default interface
should just be, "How much memory is my VM using", and balloon drivers
or paging shouldn't have to be of concern to them.  But there are
times when admins will need to dig in deeper and play with specific
values.  We should make the common case simple, and the complicated
case possible.

What about the following interface:

maxmem=X
memory=M
xenpaging=[off|on|delay]
pagingdelay=60
pagingdelayboot=180

xl mem-set domain M
 xenpaging off: Set balloon target to M
 xenpaging on: Set paging target to M
 xenpaging delay: Set balloon target to M, and wait for actual memory
to reach M.  If it hasn't reached it by $paging_delay seconds, set
balloon target to M.

xl mem-balloon-set domain M
 Set balloon target to M
xl mem-paging-set domain M
 Set paging target to M

Start-of-day:
 xenpaging off: Set balloon target to M, use PoD
 xenpaging on: ??
 xenpaging delay: Set balloon target to M, use PoD.  Wait
$pagingdelayboot seconds, if target not reached, set paging?

 -George

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