Re: [Xen-devel] [PATCH v4 16/16] libxl/arm: Add the size of ACPI tables to maxmem

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Aug 29, 2016 at 03:07:07PM -0400, Julien Grall wrote:
> Hi Shannon,
> 
> On 16/08/2016 06:25, Shannon Zhao wrote:
> >From: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> >
> >While it defines the maximum size of guest ACPI tables in guest
> >memory layout, here it adds the size to set the target maxmem
> >to avoid providing less available memory for guest.
> >
> >Signed-off-by: Shannon Zhao <shannon.zhao@xxxxxxxxxx>
> >---
> > tools/libxl/libxl_arm.c | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> >diff --git a/tools/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
> >index d436167..75b2589 100644
> >--- a/tools/libxl/libxl_arm.c
> >+++ b/tools/libxl/libxl_arm.c
> >@@ -103,6 +103,17 @@ int libxl__arch_domain_save_config(libxl__gc *gc,
> > int libxl__arch_domain_create(libxl__gc *gc, libxl_domain_config *d_config,
> >                               uint32_t domid)
> > {
> >+    libxl_domain_build_info *const info = &d_config->b_info;
> >+    libxl_ctx *ctx = libxl__gc_owner(gc);
> >+
> >+    /* Add the size of ACPI tables to maxmem if ACPI is enabled for guest. 
> >*/
> >+    if (libxl_defbool_val(info->acpi) &&
> >+        xc_domain_setmaxmem(ctx->xch, domid, info->target_memkb +
> >+        LIBXL_MAXMEM_CONSTANT + GUEST_ACPI_SIZE / 1024) < 0) {
> 
> Why can't we use the estimate size here? It would be better than increasing
> by a constant again the max size (I doubt the ACPI tables will be 2MB every
> time).
> 
> Also, this looks like quite unsafe. If someone decides to change the default
> size, (s)he would have to replicate the new algo here.
> 
> Wei, Ian, do you have any suggestion to avoid duplication?
> 

Provide a function to calculate the value needed?

> >+        LOGE(ERROR, "Couldn't set max memory");
> >+        return ERROR_FAIL;
> >+    }
> >+
> >     return 0;
> > }
> >
> >
> 
> Regards,
> 
> -- 
> Julien Grall

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