[PATCH] mm/page_alloc: call check_pcp_refill() while zone spinlock is not held

Eric Dumazet
2022-03-13T23:26:00Z

From: Eric Dumazet <edumazet@google.com>

check_pcp_refill() is used from rmqueue_bulk() while zone spinlock
is held.

This used to be fine because check_pcp_refill() was testing only the
head page, while its 'struct page' was very hot in the cpu caches.

With ("mm/page_alloc: check high-order pages for corruption during PCP
operations") check_pcp_refill() will add latencies for high order pages.

We can defer the calls to check_pcp_refill() after the zone
spinlock has been released.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
---
mm/page_alloc.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c9ebf0635d592c6f58df9793ce9fa213371a9a7f..5f0531c11ad668b1c4426ebddc17821aca824783 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3024,7 +3024,9 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
unsigned long count, struct list_head *list,
int migratetype, unsigned int alloc_flags)
{
+ struct page *page, *tmp;
int i, allocated = 0;
+ int free_cma_pages = 0;

/*
* local_lock_irq held so equivalent to spin_lock_irqsave for
@@ -3032,14 +3034,10 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
spin_lock(&zone->lock);
for (i = 0; i < count; ++i) {
- struct page *page = __rmqueue(zone, order, migratetype,
- alloc_flags);
+ page = __rmqueue(zone, order, migratetype, alloc_flags);
if (unlikely(page == NULL))
break;

- if (unlikely(check_pcp_refill(page)))
- continue;
-
/*
* Split buddy pages returned by expand() are received here in
* physical page order. The page is added to the tail of
@@ -3052,9 +3050,6 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
list_add_tail(&page->lru, list);
allocated++;
- if (is_migrate_cma(get_pcppage_migratetype(page)))
- __mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
- -(1 << order));
}

/*
@@ -3065,6 +3060,16 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
*/
__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
spin_unlock(&zone->lock);
+ list_for_each_entry_safe(page, tmp, list, lru) {
+ if (unlikely(check_pcp_refill(page))) {
+ list_del(&page->lru);
+ allocated--;
+ } else if (is_migrate_cma(get_pcppage_migratetype(page))) {
+ free_cma_pages++;
+ }
+ }
+ if (free_cma_pages)
+ __mod_zone_page_state(zone, NR_FREE_CMA_PAGES, -(free_cma_pages << order));
return allocated;
}

--
2.35.1.723.g4982287a31-goog