On 19.11.24 17:12, Zi Yan wrote:
On 19 Nov 2024, at 10:29, David Hildenbrand wrote:
+/* Split a multi-block free page into its individual pageblocks. */
+static void split_large_buddy(struct zone *zone, struct page *page,
+ unsigned long pfn, int order, fpi_t fpi)
+{
+ unsigned long end = pfn + (1 << order);
+
+ VM_WARN_ON_ONCE(!IS_ALIGNED(pfn, 1 << order));
+ /* Caller removed page from freelist, buddy info cleared! */
+ VM_WARN_ON_ONCE(PageBuddy(page));
+
+ if (order > pageblock_order)
+ order = pageblock_order;
+
+ while (pfn != end) {
+ int mt = get_pfnblock_migratetype(page, pfn);
+
+ __free_one_page(page, pfn, zone, order, mt, fpi);
+ pfn += 1 << order;
+ page = pfn_to_page(pfn);
+ }
+}
Hi,
stumbling over this while digging through the code ....
+
static void free_one_page(struct zone *zone, struct page *page,
unsigned long pfn, unsigned int order,
fpi_t fpi_flags)
{
unsigned long flags;
- int migratetype;
spin_lock_irqsave(&zone->lock, flags);
- migratetype = get_pfnblock_migratetype(page, pfn);
- __free_one_page(page, pfn, zone, order, migratetype, fpi_flags);
This change is rather undesired:
via __free_pages_core()->__free_pages_ok() we can easily end up here with order=MAX_PAGE_ORDER.
Do you have a concrete example? PMD THP on x86_64 is pageblock_order.
We do not have PMD level mTHP yet. Any other possible source?
What your new code will do is split this perfectly reasonable MAX_PAGE_ORDER chunk via split_large_buddy() into pageblock-sized chunks, and let the buddy merging logic undo our unnecessary splitting.
Is there a way to avoid this and just process the whole MAX_PAGE_ORDER chunk like we used to?
Probably split_large_buddy() can check the migratetypes of the to-be-freed
page, if order > pageblock_order. If all migratetypes are the same, the page
can be freed at MAX_PAGE_ORDER, otherwise pageblock_order.
Thinking about this: why do we care about the migratetype?
We only have to fallback to pageblocks if any pageblock is
"MIGRATE_ISOLATE" (and maybe MIGRATE_CMA), but not all. Otherwise, we
can just ignore the migratetype (or rather overwrite it)
--
Cheers,
David / dhildenb
