Re: [PATCH 2/8] xen/balloon: Move common memory reservation routines to a module

[Boris Ostrovsky]

On 05/29/2018 02:22 PM, Oleksandr Andrushchenko wrote:
> On 05/29/2018 09:04 PM, Boris Ostrovsky wrote:
>> On 05/25/2018 11:33 AM, Oleksandr Andrushchenko wrote:

>> @@ -463,11 +457,6 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>> ÂÂÂÂÂ int rc;
>> ÂÂÂÂÂ unsigned long i;
>> ÂÂÂÂÂ struct pageÂÂ *page;
>> -ÂÂÂ struct xen_memory_reservation reservation = {
>> -ÂÂÂÂÂÂÂ .address_bits = 0,
>> -ÂÂÂÂÂÂÂ .extent_order = EXTENT_ORDER,
>> -ÂÂÂÂÂÂÂ .domidÂÂÂÂÂÂÂ = DOMID_SELF
>> -ÂÂÂ };
>> Â ÂÂÂÂÂ if (nr_pages > ARRAY_SIZE(frame_list))
>> ÂÂÂÂÂÂÂÂÂ nr_pages = ARRAY_SIZE(frame_list);
>> @@ -486,9 +475,7 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>> ÂÂÂÂÂÂÂÂÂ page = balloon_next_page(page);
>> ÂÂÂÂÂ }
>> Â -ÂÂÂ set_xen_guest_handle(reservation.extent_start, frame_list);
>> -ÂÂÂ reservation.nr_extents = nr_pages;
>> -ÂÂÂ rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
>> +ÂÂÂ rc = xenmem_reservation_increase(nr_pages, frame_list);
>> ÂÂÂÂÂ if (rc <= 0)
>> ÂÂÂÂÂÂÂÂÂ return BP_EAGAIN;
>> Â @@ -496,29 +483,7 @@ static enum bp_state
>> increase_reservation(unsigned long nr_pages)
>> ÂÂÂÂÂÂÂÂÂ page = balloon_retrieve(false);
>> ÂÂÂÂÂÂÂÂÂ BUG_ON(page == NULL);
>> Â -#ifdef CONFIG_XEN_HAVE_PVMMU
>> -ÂÂÂÂÂÂÂ /*
>> -ÂÂÂÂÂÂÂÂ * We don't support PV MMU when Linux and Xen is using
>> -ÂÂÂÂÂÂÂÂ * different page granularity.
>> -ÂÂÂÂÂÂÂÂ */
>> -ÂÂÂÂÂÂÂ BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
>> -
>> -ÂÂÂÂÂÂÂ if (!xen_feature(XENFEAT_auto_translated_physmap)) {
>> -ÂÂÂÂÂÂÂÂÂÂÂ unsigned long pfn = page_to_pfn(page);
>> -
>> -ÂÂÂÂÂÂÂÂÂÂÂ set_phys_to_machine(pfn, frame_list[i]);
>> -
>> -ÂÂÂÂÂÂÂÂÂÂÂ /* Link back into the page tables if not highmem. */
>> -ÂÂÂÂÂÂÂÂÂÂÂ if (!PageHighMem(page)) {
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ int ret;
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ret = HYPERVISOR_update_va_mapping(
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ (unsigned long)__va(pfn << PAGE_SHIFT),
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ mfn_pte(frame_list[i], PAGE_KERNEL),
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ 0);
>> -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ BUG_ON(ret);
>> -ÂÂÂÂÂÂÂÂÂÂÂ }
>> -ÂÂÂÂÂÂÂ }
>> -#endif
>> +ÂÂÂÂÂÂÂ xenmem_reservation_va_mapping_update(1, &page, &frame_list[i]);
>>
>> Can you make a single call to xenmem_reservation_va_mapping_update(rc,
>> ...)? You need to keep track of pages but presumable they can be put
>> into an array (or a list). In fact, perhaps we can have
>> balloon_retrieve() return a set of pages.
> This is actually how it is used later on for dma-buf, but I just
> didn't want
> to alter original balloon code too much, but this can be done, in
> order of simplicity:
>
> 1. Similar to frame_list, e.g. static array of struct page* of size
> ARRAY_SIZE(frame_list):
> more static memory is used, but no allocations
>
> 2. Allocated at run-time with kcalloc: allocation can fail


If this is called in freeing DMA buffer code path or in error path then
we shouldn't do it.


>
> 3. Make balloon_retrieve() return a set of pages: will require
> list/array allocation
> and handling, allocation may fail, balloon_retrieve prototype change


balloon pages are strung on the lru list. Can we keep have
balloon_retrieve return a list of pages on that list?

-boris


>
> Could you please tell which of the above will fit better?
>
>>
>>