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SubjectRe: [PATCH v3 0/5] mm: Enable CONFIG_NODES_SPAN_OTHER_NODES by default for NUMA
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))
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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