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From:   Oscar Salvador <osalvador@suse.de>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     David Hildenbrand <david@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Wei Yang <richard.weiyang@gmail.com>,
        Miaohe Lin <linmiaohe@huawei.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Oscar Salvador <osalvador@suse.de>
Subject: [PATCH 1/3] mm/page_alloc: Do not calculate node's total pages and memmap pages when empty
Date:   Mon,  7 Mar 2022 16:07:23 +0100
Message-Id: <20220307150725.6810-2-osalvador@suse.de>
In-Reply-To: <20220307150725.6810-1-osalvador@suse.de>
References: <20220307150725.6810-1-osalvador@suse.de>
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free_area_init_node() calls calculate_node_totalpages() and
free_area_init_core(). The former to get node's {spanned,present}_pages,
and the latter to calculate, among other things, how many pages per zone
we spent on memmap_pages, which is used to substract zone's free pages.

On memoryless-nodes, it is pointless to perform such a bunch of work, so
make sure we skip the calculations when having a node or empty zone.

Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 mm/page_alloc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 967085c1c78a..0b7d176a8990 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7312,6 +7312,10 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 	unsigned long realtotalpages = 0, totalpages = 0;
 	enum zone_type i;
 
+	/* Skip calculation for memoryless nodes */
+	if (node_start_pfn == node_end_pfn)
+		goto no_pages;
+
 	for (i = 0; i < MAX_NR_ZONES; i++) {
 		struct zone *zone = pgdat->node_zones + i;
 		unsigned long zone_start_pfn, zone_end_pfn;
@@ -7344,6 +7348,7 @@ static void __init calculate_node_totalpages(struct pglist_data *pgdat,
 		realtotalpages += real_size;
 	}
 
+no_pages:
 	pgdat->node_spanned_pages = totalpages;
 	pgdat->node_present_pages = realtotalpages;
 	pr_debug("On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
@@ -7562,6 +7567,10 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		size = zone->spanned_pages;
 		freesize = zone->present_pages;
 
+		/* No pages? Nothing to calculate then. */
+		if (!size)
+			goto no_pages;
+
 		/*
 		 * Adjust freesize so that it accounts for how much memory
 		 * is used by this zone for memmap. This affects the watermark
@@ -7597,6 +7606,7 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		 * when the bootmem allocator frees pages into the buddy system.
 		 * And all highmem pages will be managed by the buddy system.
 		 */
+no_pages:
 		zone_init_internals(zone, j, nid, freesize);
 
 		if (!size)
-- 
2.34.1