Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
From:   Mel Gorman <mgorman@techsingularity.net>
To:     Nicolas Saenz Julienne <nsaenzju@redhat.com>
Cc:     Marcelo Tosatti <mtosatti@redhat.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 4/6] mm/page_alloc: Remove unnecessary page == NULL check in rmqueue
Date:   Wed, 20 Apr 2022 10:59:04 +0100
Message-Id: <20220420095906.27349-5-mgorman@techsingularity.net>
In-Reply-To: <20220420095906.27349-1-mgorman@techsingularity.net>
References: <20220420095906.27349-1-mgorman@techsingularity.net>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The VM_BUG_ON check for a valid page can be avoided with a simple
change in the flow. The ZONE_BOOSTED_WATERMARK is unlikely in general
and even more unlikely if the page allocation failed so mark the
branch unlikely.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/page_alloc.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 4c1acf666056..dc0fdeb3795c 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3765,17 +3765,18 @@ struct page *rmqueue(struct zone *preferred_zone,
 
 	page = rmqueue_buddy(preferred_zone, zone, order, alloc_flags,
 							migratetype);
-	if (unlikely(!page))
-		return NULL;
 
 out:
 	/* Separate test+clear to avoid unnecessary atomics */
-	if (test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags)) {
+	if (unlikely(test_bit(ZONE_BOOSTED_WATERMARK, &zone->flags))) {
 		clear_bit(ZONE_BOOSTED_WATERMARK, &zone->flags);
 		wakeup_kswapd(zone, 0, 0, zone_idx(zone));
 	}
 
-	VM_BUG_ON_PAGE(page && bad_range(zone, page), page);
+	if (unlikely(!page))
+		return NULL;
+
+	VM_BUG_ON_PAGE(bad_range(zone, page), page);
 	return page;
 }
 
-- 
2.34.1