Re: [Qemu-devel] [PATCH v5 5/6] Add memfd based hostmem

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Oct 23, 2017 at 07:41:57AM -0400, Marc-André Lureau wrote:
> 
> 
> ----- Original Message -----
> > On Mon, Oct 23, 2017 at 10:59:09AM +0100, Marc-André Lureau wrote:
> > > Add a new memory backend, similar to hostmem-file, except that it
> > > doesn't need to create files. It also enforces memory sealing.
> > > 
> > > This backend is mainly useful for sharing the memory with other
> > > processes.
> > > 
> > > Note that Linux supports transparent huge-pages of shmem/memfd memory
> > > since 4.8. It is relatively easier to set up THP than a dedicate
> > > hugepage mount point by using "madvise" in
> > > /sys/kernel/mm/transparent_hugepage/shmem_enabled.
> > > 
> > > Since 4.14, memfd allows to set hugetlb requirement explicitly.
> > > 
> > > Usage:
> > > -object memory-backend-memfd,id=mem1,size=1G
> > 
> > [snip]
> > 
> > > +static void
> > > +memfd_backend_class_init(ObjectClass *oc, void *data)
> > > +{
> > > +    HostMemoryBackendClass *bc = MEMORY_BACKEND_CLASS(oc);
> > > +
> > > +    bc->alloc = memfd_backend_memory_alloc;
> > > +
> > > +    object_class_property_add_bool(oc, "hugetlb",
> > > +                                   memfd_backend_get_hugetlb,
> > > +                                   memfd_backend_set_hugetlb,
> > > +                                   &error_abort);
> > 
> > I tend to think that instead of a bool hugetlb, we should take an
> > integer page size instead eg  hugepagesize=2M instead of hugetlb=true
> > 
> 
> Well, how would you then create a memfd without explicit hugetlb
> request or one with default hugetlb size?

Hmm, yes, libvirt would not need that, but that would be useful still for
direct QEMU users.

> I think size should be a different property. I'll add it.

Yep ok

Regards,
Daniel
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