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From:   Eric Dumazet <eric.dumazet@gmail.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Eric Dumazet <edumazet@google.com>,
        Eric Dumazet <eric.dumazet@gmail.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Matthew Wilcox <willy@infradead.org>,
        Shakeel Butt <shakeelb@google.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>, Wei Xu <weixugc@google.com>,
        Greg Thelen <gthelen@google.com>,
        Hugh Dickins <hughd@google.com>
Subject: [PATCH] mm/page_alloc: call check_pcp_refill() while zone spinlock is not held
Date:   Sun, 13 Mar 2022 16:25:47 -0700
Message-Id: <20220313232547.3843690-1-eric.dumazet@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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