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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-02-16 at 07:47 +0000, Olaf Hering wrote:
> # HG changeset patch
> # User Olaf Hering <olaf@xxxxxxxxx>
> # Date 1329378376 -3600
> # Node ID d368cf36d66c1e8df60bd0a4868c171b6a929edc
> # Parent  bf0a7c205687857a8f8d3bd3841654ed61828193
> RFC: initial libxl support for xenpaging
> 
> After the previous discussion about integration of xenpaging into xl/libxl it
> was not clear to me wether my proposal as a whole or only parts of it were
> rejected. So here is my current understanding of the comments I received.
> 
> Add initial support to libxl to start xenpaging for a HVM guest.
> These are the considerations:
> - a knob in domU.cfg is needed to start xenpaging
> - xenpaging needs a target in KiB in "memory/target-tot_pages"
>  -> the knob should be the target value in MiB: mem_target_paging=NUM
>     if the value is 0, xenpaging is not started

Wasn't the plan that the knob exported by xl should be a boolean and
that libxl should have the full value in its API, or am I
misremembering?

IOW at the libxl layer we have the full semantics available to callers
but at the xl layer we only expose one "target memory" value to users
which we expect the guest to use ballooning to reach but which we
"enforce" with paging if they don't comply.

[...] 
> - I have some ideas to add runtime tuneables for xenpaging. Should there be a
>   "xl xenpaging_ctrl tuneable_name value" command, or should it be done with a
>   new tool xenpaging_ctrl? If the latter, the proposed 'xl mem-target-*'
>   commands are not needed and this new helper could also adjust
>   "memory/target-tot_pages".

I think users would reasonably expect to always interact with the paging
daemon via the toolstack, at least for normal non-debug operations, and
so the paging daemon should not have any public interface.

Ian.



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