Subject: Re: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA

From: Baoquan He <[email-masked]>
Date: Tue, 31 Mar 2020 22:03:32 +0800

Hi Michal,

On 03/31/20 at 10:55am, Michal Hocko wrote:
> On Tue 31-03-20 11:14:23, Mike Rapoport wrote:
> > Maybe I mis-read the code, but I don't see how this could happen. In the
> > HAVE_MEMBLOCK_NODE_MAP=y case, free_area_init_node() calls
> > calculate_node_totalpages() that ensures that node->node_zones are entirely
> > within the node because this is checked in zone_spanned_pages_in_node().
> 
> zone_spanned_pages_in_node does chech the zone boundaries are within the
> node boundaries. But that doesn't really tell anything about other
> potential zones interleaving with the physical memory range.
> zone->spanned_pages simply gives the physical range for the zone
> including holes. Interleaving nodes are essentially a hole
> (__absent_pages_in_range is going to skip those).
> 
> That means that when free_area_init_core simply goes over the whole
> physical zone range including holes and that is why we need to check
> both for physical and logical holes (aka other nodes).
> 
> The life would be so much easier if the whole thing would simply iterate
> over memblocks...

The memblock iterating sounds a great idea. I tried with putting the
memblock iterating in the upper layer, memmap_init(), which is used for
boot mem only anyway. Do you think it's doable and OK? It yes, I can
work out a formal patch to make this simpler as you said. The draft code
is as below. Like this it uses the existing code and involves little change.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 138a56c0f48f..558d421f294b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6007,14 +6007,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
 		 * function.  They do not exist on hotplugged memory.
 		 */
 		if (context == MEMMAP_EARLY) {
-			if (!early_pfn_valid(pfn)) {
-				pfn = next_pfn(pfn);
-				continue;
-			}
-			if (!early_pfn_in_nid(pfn, nid)) {
-				pfn++;
-				continue;
-			}
 			if (overlap_memmap_init(zone, &pfn))
 				continue;
 			if (defer_init(nid, pfn, end_pfn))
@@ -6130,9 +6122,17 @@ static void __meminit zone_init_free_lists(struct zone *zone)
 }
 
 void __meminit __weak memmap_init(unsigned long size, int nid,
-				  unsigned long zone, unsigned long start_pfn)
+				  unsigned long zone, unsigned long range_start_pfn)
 {
-	memmap_init_zone(size, nid, zone, start_pfn, MEMMAP_EARLY, NULL);
+	unsigned long start_pfn, end_pfn;
+	unsigned long range_end_pfn = range_start_pfn + size;
+	int i;
+	for_each_mem_pfn_range(i, nid, &start_pfn, &end_pfn, NULL) {
+		start_pfn = clamp(start_pfn, range_start_pfn, range_end_pfn);
+		end_pfn = clamp(end_pfn, range_start_pfn, range_end_pfn);
+		if (end_pfn > start_pfn)
+			memmap_init_zone(size, nid, zone, start_pfn, MEMMAP_EARLY, NULL);
+	}
 }
 
 static int zone_batchsize(struct zone *zone)

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