On Wed, May 11, 2022 at 05:12:07PM +0900, Wonhyuk Yang wrote:
> Currently, trace point mm_page_alloc_zone_locked() doesn't show
> correct information.
>
> First, when alloc_flag has ALLOC_HARDER/ALLOC_CMA, page can
> be allocated from MIGRATE_HIGHATOMIC/MIGRATE_CMA. Nevertheless,
> tracepoint use requested migration type not MIGRATE_HIGHATOMIC and
> MIGRATE_CMA.
>
> Second, after Commit 44042b4498728 ("mm/page_alloc: allow high-order
> pages to be stored on the per-cpu lists") percpu-list can store
> high order pages. But trace point determine whether it is a refiil
> of percpu-list by comparing requested order and 0.
>
> To handle these problems, use cached migration type by
> get_pcppage_migratetype() instead of requested migration type.
> Then, make mm_page_alloc_zone_locked() be called only two contexts
> (rmqueue_bulk, rmqueue). With a new argument called percpu_refill,
> it can show whether it is a refill of percpu-list correctly.
>
You're definitely right that the current tracepoint is broken.
I got momentarily confused because HIGHATOMIC and CMA are not stored on
PCP lists even though they are a pageblock migrate type. Superficially
calling get_pcppage_migratetype on a page that cannot be a PCP page
seems silly but in the context of this patch, it happens to work because
it was isolated with __rmqueue_smallest which sets the PCP type even if
the page is not going to a PCP list.
The original intent of that tracepoint was to trace when pages were
removed from the buddy list. That would suggest this untested patch on
top of yours as a simplication;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0351808322ba..66a70b898130 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2476,6 +2476,8 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
del_page_from_free_list(page, zone, current_order);
expand(zone, page, order, current_order, migratetype);
set_pcppage_migratetype(page, migratetype);
+ trace_mm_page_alloc_zone_locked(page, order, migratetype,
+ pcp_allowed_order(order) && migratetype < MIGRATE_PCPTYPES);
return page;
}
@@ -3025,7 +3027,6 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
int migratetype, unsigned int alloc_flags)
{
int i, allocated = 0;
- int mt;
/*
* local_lock_irq held so equivalent to spin_lock_irqsave for
@@ -3053,9 +3054,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
list_add_tail(&page->lru, list);
allocated++;
- mt = get_pcppage_migratetype(page);
- trace_mm_page_alloc_zone_locked(page, order, mt, true);
- if (is_migrate_cma(mt))
+ if (is_migrate_cma(get_pcppage_migratetype(page)))
__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
-(1 << order));
}
@@ -3704,7 +3703,6 @@ struct page *rmqueue(struct zone *preferred_zone,
{
unsigned long flags;
struct page *page;
- int mt;
if (likely(pcp_allowed_order(order))) {
/*
@@ -3734,17 +3732,15 @@ struct page *rmqueue(struct zone *preferred_zone,
* reserved for high-order atomic allocation, so order-0
* request should skip it.
*/
- if (order > 0 && alloc_flags & ALLOC_HARDER) {
+ if (order > 0 && alloc_flags & ALLOC_HARDER)
page = __rmqueue_smallest(zone, order, MIGRATE_HIGHATOMIC);
- }
if (!page) {
page = __rmqueue(zone, order, migratetype, alloc_flags);
if (!page)
goto failed;
}
- mt = get_pcppage_migratetype(page);
- trace_mm_page_alloc_zone_locked(page, order, mt, false);
- __mod_zone_freepage_state(zone, -(1 << order), mt);
+ __mod_zone_freepage_state(zone, -(1 << order),
+ get_pcppage_migratetype(page));
spin_unlock_irqrestore(&zone->lock, flags);
} while (check_new_pages(page, order));
