Re: [Qemu-devel] [PATCH v18 13/14] memory backend: fill memory backend ram fields

[Hu Tao]

On Wed, Feb 19, 2014 at 10:36:57AM +0100, Igor Mammedov wrote:
> On Wed, 19 Feb 2014 10:03:13 +0100
> Paolo Bonzini <address@hidden> wrote:
> 
> >   19/02/2014 08:54, Hu Tao ha scritto:
> > > Thus makes user control how to allocate memory for ram backend.
> > >
> > > Signed-off-by: Hu Tao <address@hidden>
> > > ---
> > >  backends/hostmem-ram.c  | 158 
> > > ++++++++++++++++++++++++++++++++++++++++++++++++
> > >  include/sysemu/sysemu.h |   2 +
> > >  2 files changed, 160 insertions(+)
> > >
> > > diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c
> [...]
> 
> > >  static int
> > >  ram_backend_memory_init(HostMemoryBackend *backend, Error **errp)
> > >  {
> > > +    HostMemoryBackendRam *ram_backend = MEMORY_BACKEND_RAM(backend);
> > > +    int mode = ram_backend->policy;
> > > +    void *p;
> > > +    unsigned long maxnode;
> > > +
> > >      if (!memory_region_size(&backend->mr)) {
> > >          memory_region_init_ram(&backend->mr, OBJECT(backend),
> > >                                 
> > > object_get_canonical_path(OBJECT(backend)),
> > >                                 backend->size);
> > > +
> > > +        p = memory_region_get_ram_ptr(&backend->mr);
> > > +        maxnode = find_last_bit(ram_backend->host_nodes, MAX_NODES);
> > > +
> > > +        mode |= ram_backend->relative ? MPOL_F_RELATIVE_NODES :
> > > +            MPOL_F_STATIC_NODES;
> > > +        /* This is a workaround for a long standing bug in Linux'
> > > +         * mbind implementation, which cuts off the last specified
> > > +         * node. To stay compatible should this bug be fixed, we
> > > +         * specify one more node and zero this one out.
> > > +         */
> > > +        if (syscall(SYS_mbind, p, backend->size, mode,
> > > +                    ram_backend->host_nodes, maxnode + 2, 0)) {
> > 
> > This does not compile on non-Linux; also, does libnuma include the 
> > workaround?  If so, this is a hint that we should be using libnuma 
> > instead...
> > 
> > Finally, all this code should be in hostmem.c, not hostmem-ram.c, 
> > because the same policies can be applied to hugepage-backed memory.
> > 
> > Currently host_memory_backend_get_memory is calling bc->memory_init. 
> > Probably the call should be replaced by something like
> I've pushed to github updated version of memdev, where
> host_memory_backend_get_memory() is just convenience wrapper to get
> access to memdev's internal MemoryRegion.
> 
> All initialization now is done in user_creatable->complete() method
> which calls ram_backend_memory_init() so leaving it as is should be fine.

There is a problem that user_creatable_complete() is called before
adding object to "/objects" (see object_create()), which triggers a
assert failure when calling object_get_canonical_path() in
ram_backend_memory_init(). Any ideas?