Re: [Xen-devel] libxl/xl memory paging/sharing/ballooning/etc proposal.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-03-15 at 15:26 +0000, Olaf Hering wrote:
> On Thu, Mar 15, Andres Lagar-Cavilla wrote:
> 
> 
> > > libxl_domain_(set|get)_paging_target(ctx, domid, target_memkb, relative)
> > >
> > >         Read/write whichever XS path controls the xenpaging daemon's
> > >         target. (Olaf?). I think this path should not be
> > >         under /local/domain since it should not be guest visible
> > >         (probably it already isn't).
> > It is /local/domain/X/memory/target-tot_pages. I agree it should not be
> > guest visible, and we're still in time to change it.
> 
> Is it guest visible? I think the entry point for a guest is /vm/<uuid>/,
> I'm almost sure it can not get to /local/domain/X/memory/

/local/domain/X is generally considered to be part of the "guest
visible" state and there are various guest visible things there,
devices/* and memory/target spring to mind.

> > /libxl/X/memory-policy/paging-target? Is there a non-libxl
> > non-/local/domain path xenpaging could look into, should it be launched
> > autonomously? Olaf, do you care about xenpaging in non-libxl environments?
> 
> xenpaging needs to read its target from somewhere, I dont think this has
> anything todo with libxl or not.

Except that libxl needs to know where to write to.

> > >         XXX libxl_domain_paging_enable here or on domain build / policy
> > >         set? libxl_domain_paging_enable is idempotent so calling it here
> > >         is always safe?
> > 
> > You can enable the pager on build, unless the actor settings preclude it.
> > Then all you need to do to get the pager to work is write its xenstore
> > key.
> > 
> > But generally speaking, the pager might have been disabled ex xl-machina,
> > so you really want to be able to test_and_set the pager here.
> > 
> > Olaf, does xenpaging have standard daemonize behavior of locking a
> > /var/foo/pid file?
> 
> It writes its pid to xenstore and announces its state in
> xenpaging/state, like qemu-dm does. Thats in my libxl support patch at
> least.

This sounds good to me.



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