Re: [Xen-devel] [PATCH v6 16/16] libxl/arm: Add the size of ACPI tables to maxmem

[Shannon Zhao <shannon.zhao@xxxxxxxxxx>]

On 2016/9/27 9:35, Wei Liu wrote:
> On Tue, Sep 27, 2016 at 09:01:00AM -0700, Shannon Zhao wrote:
> > On 2016/9/27 2:41, Wei Liu wrote:
> > > On Mon, Sep 26, 2016 at 02:54:55PM -0700, Shannon Zhao wrote:
> > > > On 2016/9/22 7:10, Wei Liu wrote:
> > > > > > diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
> > > > > > > index 2924629..118beab 100644
> > > > > > > --- a/tools/libxl/libxl_dom.c
> > > > > > > +++ b/tools/libxl/libxl_dom.c
> > > > > > > @@ -408,8 +408,15 @@ int libxl__build_pre(libxl__gc *gc, uint32_t domid,
> > > > > > >         }
> > > > > > >     }
> > > > > > >
> > > > > > > +
> > > > > > > +    rc = libxl__arch_memory_constant(gc, info, state);
> > > > > > > +    if (rc < 0) {
> > > > > > > +        LOGE(ERROR, "Couldn't get arch constant memory size");
> > > > > > > +        return ERROR_FAIL;
> > > > > > > +    }
> > > > > > > +
> > > > > > >     if (xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb +
> > > > > > > -        LIBXL_MAXMEM_CONSTANT) < 0) {
> > > > > > > +        LIBXL_MAXMEM_CONSTANT + rc) < 0) {
> > > > > I think this LIBXL_MAXMEM_CONSTANT should be pushed to your helper
> > > > > function, too.
> > > > >
> > > > > So that, we can have all LIBXL_MAXMEM_CONSTANT removed in libxl
> > > > > functions (see libxl.c and libxl_dom.c)
> > > > If we push LIBXL_MAXMEM_CONSTANT to the libxl_arch_memory_constant and
> > > > remove it from libxl.c, do we need to call libxl_arch_memory_constant there
> > > > in libxl_set_memory_target()?
> > > Yes, we need to call that function everywhere to get consistent results.
> > > That's the reason I asked you to consolidate it to a function.
> > Well it's a little awkward I think, since in libxl_domain_setmaxmem() and
> > libxl_set_memory_target() it seems it can't get the parameters info and
> > state for libxl__arch_memory_constant().
> > I'm not sure how to solve it. Wei, any suggestion?
> Hmm...
>
> The first question is can state be derived from build_info ? From my
> quick skim of the code the answer is likely yes.
I'm not familiar with the relationship between these structures and not 
sure how to do this. Please give me some suggestion.
> Then, you can call libxl_retrieve_domain_configuration to get
> domain_config, then domain_config->build_info, so that you can derive
> state from it.
>
> Feel free to ask more questions.
>
> Without such arrangement, ballooning is going to be broken for ARM
> guests.
I see.

Thanks,
--
Shannon

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