On 05/29/2018 11:03 PM, Boris Ostrovsky wrote:
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)
int rc;
unsigned long i;
struct page *page;
- struct xen_memory_reservation reservation = {
- .address_bits = 0,
- .extent_order = EXTENT_ORDER,
- .domid = DOMID_SELF
- };
if (nr_pages > ARRAY_SIZE(frame_list))
nr_pages = ARRAY_SIZE(frame_list);
@@ -486,9 +475,7 @@ static enum bp_state
increase_reservation(unsigned long nr_pages)
page = balloon_next_page(page);
}
- set_xen_guest_handle(reservation.extent_start, frame_list);
- reservation.nr_extents = nr_pages;
- rc = HYPERVISOR_memory_op(XENMEM_populate_physmap, &reservation);
+ rc = xenmem_reservation_increase(nr_pages, frame_list);
if (rc <= 0)
return BP_EAGAIN;
@@ -496,29 +483,7 @@ static enum bp_state
increase_reservation(unsigned long nr_pages)
page = balloon_retrieve(false);
BUG_ON(page == NULL);
-#ifdef CONFIG_XEN_HAVE_PVMMU
- /*
- * We don't support PV MMU when Linux and Xen is using
- * different page granularity.
- */
- BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE);
-
- if (!xen_feature(XENFEAT_auto_translated_physmap)) {
- unsigned long pfn = page_to_pfn(page);
-
- set_phys_to_machine(pfn, frame_list[i]);
-
- /* Link back into the page tables if not highmem. */
- if (!PageHighMem(page)) {
- int ret;
- ret = HYPERVISOR_update_va_mapping(
- (unsigned long)__va(pfn << PAGE_SHIFT),
- mfn_pte(frame_list[i], PAGE_KERNEL),
- 0);
- BUG_ON(ret);
- }
- }
-#endif
+ 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?
First of all, before we go deep in details, I will highlight
the goal of the requested change: for balloon driver we call
xenmem_reservation_va_mapping_update(*1*, &page, &frame_list[i]);
from increase_reservation
and
xenmem_reservation_va_mapping_reset(*1*, &page);
from decrease_reservation and it seems to be not elegant because of
that one page/frame passed while we might have multiple pages/frames
passed at once.
In the balloon driver the producer of pages for increase_reservation
is balloon_retrieve(false) and for decrease_reservation it is
alloc_page(gfp).
In case of decrease_reservation the page is added on the list:
LIST_HEAD(pages);
[...]
list_add(&page->lru, &pages);
and in case of increase_reservation it is retrieved page by page
and can be put on a list as well with the same code from
decrease_reservation, e.g.
LIST_HEAD(pages);
[...]
list_add(&page->lru, &pages);
Thus, both decrease_reservation and increase_reservation may hold
their pages on a list before calling
xenmem_reservation_va_mapping_{update|reset}.
For that we need a prototype change:
xenmem_reservation_va_mapping_reset(<nr_pages>, <list of pages>);
But for xenmem_reservation_va_mapping_update it will look like:
xenmem_reservation_va_mapping_update(<nr_pages>, <list of pages>, <array
of frames>)
which seems to be inconsistent. Converting entries of the static
frame_list array
into corresponding list doesn't seem to be cute as well.
For dma-buf use-case arrays are more preferable as dma-buf constructs
scatter-gather
tables from array of pages etc. and if page list is passed then it needs
to be
converted into page array anyways.
So, we can:
1. Keep the prototypes as is, e.g. accept array of pages and use
nr_pages == 1 in
case of balloon driver (existing code)
2. Statically allocate struct page* array in the balloon driver and fill
it with pages
when those pages are retrieved:
static struct page *page_list[ARRAY_SIZE(frame_list)];
which will take additional 8KiB of space on 64-bit platform, but
simplify things a lot.
3. Allocate struct page *page_list[ARRAY_SIZE(frame_list)] dynamically
As to Boris' suggestion "balloon pages are strung on the lru list. Can
we keep have
balloon_retrieve return a list of pages on that list?"
Because of alloc_xenballooned_pages' retry logic for page retireval, e.g.
while (pgno < nr_pages) {
page = balloon_retrieve(true);
if (page) {
[...]
} else {
ret = add_ballooned_pages(nr_pages - pgno);
[...]
}
I wouldn't change things that much.
IMO, we can keep 1 page based API with the only overhead for balloon
driver of
function calls to xenmem_reservation_va_mapping_{update|reset} for each
page.
-boris
Thank you,
Oleksandr
Could you please tell which of the above will fit better?
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