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