From aed8533b71e373a963b3037dff4bca4c7bec2a83 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Tue, 6 Jun 2017 15:50:18 +0200
Subject: [PATCH 1/4] mm, memory_hotplug: simplify empty node mask handling in
 new_node_page
Git-commit: 7f252f277b66854c61d3abdd4c196d6dc64fa333
Patch-mainline: v4.13-rc1
References: bnc#1042553

new_node_page tries to allocate the target page on a different NUMA node
than the source page. This makes sense in most cases during the hotplug
because we are likely to offline the whole numa node. But there are
cases where there are no other nodes to fallback (e.g. when offlining
parts of the only existing node) and we have to fallback to allocating
from the source node. The current code does that but it can be
simplified by checking the nmask and updating it before we even try to
allocate rather than special casing it.

This patch shouldn't introduce any functional change.

Signed-off-by: Michal Hocko <mhocko@suse.com>

---
 mm/memory_hotplug.c |   22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1358,7 +1358,15 @@ static struct page *new_node_page(struct
 	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
 	int nid = page_to_nid(page);
 	nodemask_t nmask = node_states[N_MEMORY];
-	struct page *new_page = NULL;
+
+	/*
+	 * try to allocate from a different node but reuse this node if there
+	 * are no other online nodes to be used (e.g. we are offlining a part
+	 * of the only existing node)
+	 */
+	node_clear(nid, nmask);
+	if (nodes_empty(nmask))
+		node_set(nid, nmask);
 
 	/*
 	 * TODO: allocate a destination hugepage from a nearest neighbor node,
@@ -1369,20 +1377,12 @@ static struct page *new_node_page(struct
 		return alloc_huge_page_node(page_hstate(compound_head(page)),
 					next_node_in(nid, nmask));
 
-	node_clear(nid, nmask);
-
 	if (PageHighMem(page)
 	    || (zone_idx(page_zone(page)) == ZONE_MOVABLE))
 		gfp_mask |= __GFP_HIGHMEM;
 
-	if (!nodes_empty(nmask))
-		new_page = __alloc_pages_nodemask(gfp_mask, 0,
-					node_zonelist(nid, gfp_mask), &nmask);
-	if (!new_page)
-		new_page = __alloc_pages(gfp_mask, 0,
-					node_zonelist(nid, gfp_mask));
-
-	return new_page;
+	return __alloc_pages_nodemask(gfp_mask, 0,
+			node_zonelist(nid, gfp_mask), &nmask);
 }
 
 #define NR_OFFLINE_AT_ONCE_PAGES	(256)