[Xen-devel] RE: xl features missing

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 19 Jul 2010, Stefano Stabellini wrote:
> On Fri, 16 Jul 2010, Dan Magenheimer wrote:
> > > From: Dan Magenheimer
> > > Subject: xl features missing
> > > 
> > > FYI, I finally got a chance to play with xl a bit in
> > > xen-unstable and quickly discovered the following:
> > 
> > > - xl create doesn't handle the possibility that tmem
> > >   has memory which is freeable (xm create does)
> > 
> > This appears to be an indicator of a bigger issue unless
> > there is some code somewhere I am missing.
> > 
> > Can "xl create" deal with ballooning memory from dom0, as is
> > done in the free() method in tools/python/xen/xend/balloon.py?
> > If not, doesn't that mean that xl is useless on systems
> > where dom0_mem= isn't specified as a boot option?
> >
> > Since tmem leverages this method to recover freeable
> > memory when creating a new guest, tmem also needs this
> > else xl is also useless on a tmem-enabled system.
> > 
> > And in either case, it appears that the error handling
> > for "out of memory" spews meaningless error messages.
> 
> xl doesn't have an equivalent of the free() method in xend, so it would
> be useless without dom0_mem= at the moment.
> However reimplementing that method shouldn't be hard, the only problem
> is that it would probably require some sort of global locking among all
> the various xl processes running concurrently.
> Maybe we need a lockfile?
> 

Another possible course of action would be to implement a libxl funtion
that calculates the amount of memory that needs to be freed, then call a
new libxl funtion similar to libxl_set_memory_target but that would take
a relative amount of memory as argument and would also be "tmem
enabled".
Finally the actual implementation of this function must communicate
relative amounts of memory to the kernel so that we can avoid the global
lock.
Does that make sense?


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