Re: [Xen-devel] [PATCH v2 12/20] xen/balloon: Don't rely on the page granularity is the same for Xen and Linux

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 17/07/15 15:03, Stefano Stabellini wrote:
>> ---
>>  drivers/xen/balloon.c | 147 
>> +++++++++++++++++++++++++++++++++++---------------
>>  1 file changed, 105 insertions(+), 42 deletions(-)
>>
>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c
>> index fd93369..19a72b1 100644
>> --- a/drivers/xen/balloon.c
>> +++ b/drivers/xen/balloon.c
>> @@ -230,6 +230,7 @@ static enum bp_state reserve_additional_memory(long 
>> credit)
>>      nid = memory_add_physaddr_to_nid(hotplug_start_paddr);
>>  
>>  #ifdef CONFIG_XEN_HAVE_PVMMU
>> +    /* TODO */
> 
> I think you need to be more verbose than that: TODO what?

It was for me to remember fixing reserve_additional_memory. I did it and
forgot to remove the TODO when I clean up.

I will drop it in the next version.

[...]

>>  static enum bp_state increase_reservation(unsigned long nr_pages)
>>  {
>>      int rc;
>> -    unsigned long  pfn, i;
>> +    unsigned long i, frame_idx;
>>      struct page   *page;
>>      struct xen_memory_reservation reservation = {
>>              .address_bits = 0,
>> @@ -343,44 +406,43 @@ static enum bp_state increase_reservation(unsigned 
>> long nr_pages)
>>      }
>>  #endif
>>  
>> -    if (nr_pages > ARRAY_SIZE(frame_list))
>> -            nr_pages = ARRAY_SIZE(frame_list);
>> +    if (nr_pages > (ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE))
>> +            nr_pages = ARRAY_SIZE(frame_list) / XEN_PFN_PER_PAGE;
>>  
>> +    frame_idx = 0;
>>      page = list_first_entry_or_null(&ballooned_pages, struct page, lru);
>>      for (i = 0; i < nr_pages; i++) {
>>              if (!page) {
>>                      nr_pages = i;
>>                      break;
>>              }
>> -            frame_list[i] = page_to_pfn(page);
>> +
>> +            rc = xen_apply_to_page(page, set_frame, &frame_idx);
>> +
>>              page = balloon_next_page(page);
>>      }
>>  
>>      set_xen_guest_handle(reservation.extent_start, frame_list);
>> -    reservation.nr_extents = nr_pages;
>> +    reservation.nr_extents = nr_pages * XEN_PFN_PER_PAGE;
>>      rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
>>      if (rc <= 0)
>>              return BP_EAGAIN;
>>  
>> -    for (i = 0; i < rc; i++) {
>> +    /* rc is equal to the number of Xen page populated */
>> +    nr_pages = rc / XEN_PFN_PER_PAGE;
> 
> Here we are purposedly ignoring any spares (rc % XEN_PFN_PER_PAGE).
> Instead of leaking them, maybe we should givem them back to Xen since we
> cannot use them?

I will give a look to do it.

>> +    for (i = 0; i < nr_pages; i++) {
>>              page = balloon_retrieve(false);
>>              BUG_ON(page == NULL);
>>  
>> -            pfn = page_to_pfn(page);
>> -
>>  #ifdef CONFIG_XEN_HAVE_PVMMU
>> +            frame_idx = 0;
> 
> Shouldn't this be before the beginning of the loop above?

Hmmmm... Yes. Note that I only compiled tested on x86, it would be good
if someone test on real hardware at some point (I don't have any x86 Xen
setup).

Regards,

-- 
Julien Grall

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