mm: default to node zonelist ordering when nodes have only lowmem

There are two types of zonelist ordering methodologies: - node order, preferring allocations on a node to stay local to and - zone order, preferring allocations come from a higher zone to avoid allocating in lowmem zones even though they may not be local. The ordering technique used by the kernel is configurable on the command line, but also has some logic to determine what the default should be. This logic currently lacks knowledge of systems where a node may only have lowmem. For such systems, it is necessary to use node order so that GFP_KERNEL allocations may be satisfied by nodes consisting of only lowmem. If zone order is used, GFP_KERNEL allocations to such nodes are actually allocated on a node with local affinity that includes ZONE_NORMAL. This change defaults to node zonelist ordering if any node lacks ZONE_NORMAL. To force zone order, append 'numa_zonelist_order=zone' to the kernel command line. Signed-off-by: David Rientjes <rientjes@google.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm: default to node zonelist ordering when nodes have only lowmem
There are two types of zonelist ordering methodologies: - node order, preferring allocations on a node to stay local to and - zone order, preferring allocations come from a higher zone to avoid allocating in lowmem zones even though they may not be local. The ordering technique used by the kernel is configurable on the command line, but also has some logic to determine what the default should be. This logic currently lacks knowledge of systems where a node may only have lowmem. For such systems, it is necessary to use node order so that GFP_KERNEL allocations may be satisfied by nodes consisting of only lowmem. If zone order is used, GFP_KERNEL allocations to such nodes are actually allocated on a node with local affinity that includes ZONE_NORMAL. This change defaults to node zonelist ordering if any node lacks ZONE_NORMAL. To force zone order, append 'numa_zonelist_order=zone' to the kernel command line. Signed-off-by: David Rientjes <rientjes@google.com> Acked-by: Mel Gorman <mel@csn.ul.ie> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
David Rientjes · Linus Torvalds
1 parent 1a5cb81465
Showing 1 changed file with 10 additions and 1 deletions Side-by-side Diff
mm/page_alloc.c
@@ -2606,7 +2606,7 @@
          * ZONE_DMA and ZONE_DMA32 can be very small area in the system.
 	 * If they are really small and used heavily, the system can fall
 	 * into OOM very easily.
-	 * This function detect ZONE_DMA/DMA32 size and confgigures zone order.
+	 * This function detect ZONE_DMA/DMA32 size and configures zone order.
 	 */
 	/* Is there ZONE_NORMAL ? (ex. ppc has only DMA zone..) */
 	low_kmem_size = 0;
@@ -2618,6 +2618,15 @@
 				if (zone_type < ZONE_NORMAL)
 					low_kmem_size += z->present_pages;
 				total_size += z->present_pages;
+			} else if (zone_type == ZONE_NORMAL) {
+				/*
+				 * If any node has only lowmem, then node order
+				 * is preferred to allow kernel allocations
+				 * locally; otherwise, they can easily infringe
+				 * on other nodes when there is an abundance of
+				 * lowmem available to allocate from.
+				 */
+				return ZONELIST_ORDER_NODE;
 			}
 		}
 	}
...	...	@@ -2606,7 +2606,7 @@
2606	2606	* ZONE_DMA and ZONE_DMA32 can be very small area in the system.
2607	2607	* If they are really small and used heavily, the system can fall
2608	2608	* into OOM very easily.
2609		- * This function detect ZONE_DMA/DMA32 size and confgigures zone order.
	2609	+ * This function detect ZONE_DMA/DMA32 size and configures zone order.
2610	2610	*/
2611	2611	/* Is there ZONE_NORMAL ? (ex. ppc has only DMA zone..) */
2612	2612	low_kmem_size = 0;
...	...	@@ -2618,6 +2618,15 @@
2618	2618	if (zone_type < ZONE_NORMAL)
2619	2619	low_kmem_size += z->present_pages;
2620	2620	total_size += z->present_pages;
	2621	+ } else if (zone_type == ZONE_NORMAL) {
	2622	+ /*
	2623	+ * If any node has only lowmem, then node order
	2624	+ * is preferred to allow kernel allocations
	2625	+ * locally; otherwise, they can easily infringe
	2626	+ * on other nodes when there is an abundance of
	2627	+ * lowmem available to allocate from.
	2628	+ */
	2629	+ return ZONELIST_ORDER_NODE;
2621	2630	}
2622	2631	}
2623	2632	}