Re: [Qemu-devel] [PATCH qemu] vmstate: Define VARRAY with VMS_ALLOC

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Mar 15, 2016 at 12:01:04PM +0000, Dr. David Alan Gilbert wrote:
> * Alexey Kardashevskiy (aik@ozlabs.ru) wrote:
> > This allows dynamic allocation for migrating arrays.
> > 
> > Already existing VMSTATE_VARRAY_UINT32 requires an array to be
> > pre-allocated, however there are cases when the size is not known in
> > advance and there is no real need to enforce it.
> > 
> > This defines another variant of VMSTATE_VARRAY_UINT32 with WMS_ALLOC
> > flag which tells the receiving side to allocate memory for the array
> > before receiving the data.
> > 
> > The first user of it is the "pseries" machine (POWER8) with
> > dynamic DMA windows which existence and size are totally dynamic.
> 
> You say totally dynamic, how big do they get out of interest?

They're basically used to map all guest RAM.  Typically we'd be
looking at one 64-bit TCE per 64K guest page, so we'd be looking at
1/8192th of RAM size.

Since we can in theory have guests in the 1T+ range, that might start
getting pretty big, so we probably should look at incremental transfer
of the TCE tables at some point.

> 
> Dave
> 
> > 
> > Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> > Reviewed-by: Thomas Huth <thuth@redhat.com>
> > ---
> > 
> > 
> > As David suggested, I am posting it alone (separately from the DDW patchset).
> > 
> > It would be nice either to get "ack" to get this pulled via the powerpc
> > tree or get it pulled to the upstream via some other tree. Thanks!
> > 
> > 
> > 
> > ---
> >  include/migration/vmstate.h | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
> > index 84ee355..1622638 100644
> > --- a/include/migration/vmstate.h
> > +++ b/include/migration/vmstate.h
> > @@ -386,6 +386,16 @@ extern const VMStateInfo vmstate_info_bitmap;
> >      .offset     = vmstate_offset_pointer(_state, _field, _type),     \
> >  }
> >  
> > +#define VMSTATE_VARRAY_UINT32_ALLOC(_field, _state, _field_num, _version, _info, _type) {\
> > +    .name       = (stringify(_field)),                               \
> > +    .version_id = (_version),                                        \
> > +    .num_offset = vmstate_offset_value(_state, _field_num, uint32_t),\
> > +    .info       = &(_info),                                          \
> > +    .size       = sizeof(_type),                                     \
> > +    .flags      = VMS_VARRAY_UINT32|VMS_POINTER|VMS_ALLOC,           \
> > +    .offset     = vmstate_offset_pointer(_state, _field, _type),     \
> > +}
> > +
> >  #define VMSTATE_VARRAY_UINT16_UNSAFE(_field, _state, _field_num, _version, _info, _type) {\
> >      .name       = (stringify(_field)),                               \
> >      .version_id = (_version),                                        \

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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