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mm/memory_hotplug: make shrink_zone_span() more robust

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Let's make shrink_zone_span() more robust by checking in
find_smallest_section_pfn() / find_biggest_section_pfn() that the
start or end PFN of the subsection is within the zone.

While at it, clean up the function by factoring the core check out
into subsection_overlaps_zone().

There likely is no need to check the nid first. We require
SPARSEMEM_VMEMMAP_ENABLE, where pfn_to_page() is cheap, and
pfn_to_nid() on CONFIG_NUMA would call pfn_to_page() either way.
So let's just drop that for now.

Tested-by: Yuan Liu <yuan1.liu@intel.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Link: https://patch.msgid.link/20260920084946.3266279-2-yuan1.liu@intel.com
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
This commit is contained in:
David Hildenbrand (Arm) 2026-09-20 04:49:45 -04:00
parent 93f51579e7
commit 1a3fed3487
1 changed files with 25 additions and 36 deletions
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61
mm/memory_hotplug.c
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@ -425,49 +425,39 @@ int __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
return err;
}
static bool subsection_overlaps_zone(unsigned long pfn, struct zone *zone)
{
const unsigned long start_pfn = ALIGN_DOWN(pfn, PAGES_PER_SUBSECTION);
const unsigned long end_pfn = start_pfn + PAGES_PER_SUBSECTION - 1;
/* All pages in a subsection are either online or offline. */
if (unlikely(!pfn_to_online_page(start_pfn)))
return false;
/* Checking start+end is sufficient. */
return zone == page_zone(pfn_to_page(start_pfn)) ||
zone == page_zone(pfn_to_page(end_pfn));
}
/* find the smallest valid pfn in the range [start_pfn, end_pfn) */
static unsigned long find_smallest_section_pfn(int nid, struct zone *zone,
unsigned long start_pfn,
unsigned long end_pfn)
static unsigned long find_smallest_section_pfn(struct zone *zone,
unsigned long start_pfn, unsigned long end_pfn)
{
for (; start_pfn < end_pfn; start_pfn += PAGES_PER_SUBSECTION) {
if (unlikely(!pfn_to_online_page(start_pfn)))
continue;
if (unlikely(pfn_to_nid(start_pfn) != nid))
continue;
if (zone != page_zone(pfn_to_page(start_pfn)))
continue;
return start_pfn;
if (subsection_overlaps_zone(start_pfn, zone))
return start_pfn;
}
return 0;
}
/* find the biggest valid pfn in the range [start_pfn, end_pfn). */
static unsigned long find_biggest_section_pfn(int nid, struct zone *zone,
unsigned long start_pfn,
unsigned long end_pfn)
static unsigned long find_biggest_section_pfn(struct zone *zone,
unsigned long start_pfn, unsigned long end_pfn)
{
unsigned long pfn;
/* pfn is the end pfn of a memory section. */
pfn = end_pfn - 1;
for (; pfn >= start_pfn; pfn -= PAGES_PER_SUBSECTION) {
if (unlikely(!pfn_to_online_page(pfn)))
continue;
if (unlikely(pfn_to_nid(pfn) != nid))
continue;
if (zone != page_zone(pfn_to_page(pfn)))
continue;
return pfn;
for (; end_pfn > start_pfn; end_pfn -= PAGES_PER_SUBSECTION) {
if (subsection_overlaps_zone(end_pfn - 1, zone))
return end_pfn - 1;
}
return 0;
}
@ -475,7 +465,6 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
unsigned long end_pfn)
{
unsigned long pfn;
int nid = zone_to_nid(zone);
if (zone->zone_start_pfn == start_pfn) {
/*
@ -484,7 +473,7 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
* In this case, we find second smallest valid mem_section
* for shrinking zone.
*/
pfn = find_smallest_section_pfn(nid, zone, end_pfn,
pfn = find_smallest_section_pfn(zone, end_pfn,
zone_end_pfn(zone));
if (pfn) {
zone->spanned_pages = zone_end_pfn(zone) - pfn;
@ -500,7 +489,7 @@ static void shrink_zone_span(struct zone *zone, unsigned long start_pfn,
* In this case, we find second biggest valid mem_section for
* shrinking zone.
*/
pfn = find_biggest_section_pfn(nid, zone, zone->zone_start_pfn,
pfn = find_biggest_section_pfn(zone, zone->zone_start_pfn,
start_pfn);
if (pfn)
zone->spanned_pages = pfn - zone->zone_start_pfn + 1;