[libvirt] [Qemu-devel] [PATCH] deprecate -mem-path fallback to anonymous RAM

[Daniel P. Berrangé]

On Mon, Jun 24, 2019 at 10:17:33AM +0200, Markus Armbruster wrote:
> Igor Mammedov <imammedo at redhat.com> writes:
> 
> > Fallback might affect guest or worse whole host performance
> > or functionality if backing file were used to share guest RAM
> > with another process.
> >
> > Patch deprecates fallback so that we could remove it in future
> > and ensure that QEMU will provide expected behavior and fail if
> > it can't use user provided backing file.
> >
> > Signed-off-by: Igor Mammedov <imammedo at redhat.com>
> > ---
> > PS:
> > Patch is written on top of
> >   [PATCH v4 0/3] numa: deprecate '-numa node,  mem' and default memory distribution
> > to avoid conflicts in qemu-deprecated.texi
> >
> >  numa.c               | 4 ++--
> >  qemu-deprecated.texi | 8 ++++++++
> >  2 files changed, 10 insertions(+), 2 deletions(-)
> >
> > diff --git a/numa.c b/numa.c
> > index 91a29138a2..53d67b8ad9 100644
> > --- a/numa.c
> > +++ b/numa.c
> > @@ -494,8 +494,8 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner,
> >              if (mem_prealloc) {
> >                  exit(1);
> >              }
> > -            error_report("falling back to regular RAM allocation.");
> > -
> > +            warn_report("falling back to regular RAM allocation. "
> > +                        "Fallback to RAM allocation is deprecated.");
> 
> Can we give the user clues on how to avoid the deprecated fallback?

There's nothing a user can do aside from ensuring they have sufficient
free memory before launching QEMU to satisfy the huge pag request.

Probably just needs changing to do.

    "This is deprecated, future QEMU releases will exit when
     huge pages cannot be allocated"

Regards,
Daniel
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