[PATCH v2 1/2] mm/page_alloc: Do not calculate node's total pages and memmap pages when empty

[Oscar Salvador <osalvador@suse.de>]

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 | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e008a3df0485..2b9b2422ba32 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -7361,6 +7361,10 @@ 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 (pgdat_is_empty(pgdat))
+		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;
@@ -7393,6 +7397,7 @@ 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);
@@ -7610,6 +7615,12 @@ 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) {
+			zone_init_internals(zone, j, nid, 0);
+			continue;
+		}
+
 		/*
 		 * Adjust freesize so that it accounts for how much memory
 		 * is used by this zone for memmap. This affects the watermark
@@ -7647,9 +7658,6 @@ static void __init free_area_init_core(struct pglist_data *pgdat)
 		 */
 		zone_init_internals(zone, j, nid, freesize);
 
-		if (!size)
-			continue;
-
 		set_pageblock_order();
 		setup_usemap(zone);
 		init_currently_empty_zone(zone, zone->zone_start_pfn, size);
@@ -7730,7 +7738,7 @@ static void __init free_area_init_node(int nid)
 	pgdat->node_start_pfn = start_pfn;
 	pgdat->per_cpu_nodestats = NULL;
 
-	if (start_pfn != end_pfn) {
+	if (!pgdat_is_empty(pgdat)) {
 		pr_info("Initmem setup node %d [mem %#018Lx-%#018Lx]\n", nid,
 			(u64)start_pfn << PAGE_SHIFT,
 			end_pfn ? ((u64)end_pfn << PAGE_SHIFT) - 1 : 0);
-- 
2.35.3