[PATCH 15/49] mm/hugetlb: free cross-zone bootmem gigantic pages after allocation

[Muchun Song]

After moving hugetlb reservation after free_area_init(), zone information
becomes available during bootmem huge page allocation. This allows us to
identify and handle cross-zone gigantic pages more precisely.

During alloc_bootmem(), pages that intersect multiple zones are added to
the head of huge_boot_pages[nid] list (without ZONES_VALID flag), while
pages with valid zones are added to the tail (with ZONES_VALID flag).

After allocation completes, hugetlb_free_cross_zone_pages() iterates
through the list and frees those cross-zone pages (entries without
HUGE_BOOTMEM_ZONES_VALID flag). The count of freed pages is subtracted
from the allocated count to ensure the final number reflects only valid
huge pages.

This applies to both per-node allocation path and the global gigantic
allocation path, simplifying the code by avoiding cross-zone checks at
later stages.

Signed-off-by: Muchun Song <songmuchun at bytedance.com>
---
 mm/hugetlb.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 47 insertions(+), 6 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index d6ea11113f1d..238495fd04e4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3049,6 +3049,11 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
 	return ERR_PTR(-ENOSPC);
 }
 
+static bool __init hugetlb_bootmem_page_earlycma(struct huge_bootmem_page *m)
+{
+	return m->flags & HUGE_BOOTMEM_CMA;
+}
+
 static __init void *alloc_bootmem(struct hstate *h, int nid, bool node_exact)
 {
 	struct huge_bootmem_page *m;
@@ -3092,7 +3097,14 @@ static __init void *alloc_bootmem(struct hstate *h, int nid, bool node_exact)
 		 * is not up yet.
 		 */
 		INIT_LIST_HEAD(&m->list);
-		list_add(&m->list, &huge_boot_pages[listnode]);
+		if (pfn_range_intersects_zones(listnode, PHYS_PFN(virt_to_phys(m)),
+					       pages_per_huge_page(h))) {
+			VM_BUG_ON(hugetlb_bootmem_page_earlycma(m));
+			list_add(&m->list, &huge_boot_pages[listnode]);
+		} else {
+			list_add_tail(&m->list, &huge_boot_pages[listnode]);
+			m->flags |= HUGE_BOOTMEM_ZONES_VALID;
+		}
 		m->hstate = h;
 	}
 
@@ -3186,11 +3198,6 @@ static bool __init hugetlb_bootmem_page_prehvo(struct huge_bootmem_page *m)
 	return m->flags & HUGE_BOOTMEM_HVO;
 }
 
-static bool __init hugetlb_bootmem_page_earlycma(struct huge_bootmem_page *m)
-{
-	return m->flags & HUGE_BOOTMEM_CMA;
-}
-
 /*
  * memblock-allocated pageblocks might not have the migrate type set
  * if marked with the 'noinit' flag. Set it to the default (MIGRATE_MOVABLE)
@@ -3393,6 +3400,34 @@ static void __init gather_bootmem_prealloc(void)
 	padata_do_multithreaded(&job);
 }
 
+static unsigned long __init hugetlb_free_cross_zone_pages(struct hstate *h, int nid)
+{
+	unsigned long freed = 0;
+	struct huge_bootmem_page *m, *tmp;
+
+	if (!hstate_is_gigantic(h))
+		return freed;
+
+	list_for_each_entry_safe(m, tmp, &huge_boot_pages[nid], list) {
+		if (m->flags & HUGE_BOOTMEM_ZONES_VALID)
+			break;
+
+		list_del(&m->list);
+		memblock_free(m, huge_page_size(h));
+		freed++;
+	}
+
+	if (freed) {
+		char buf[32];
+
+		string_get_size(huge_page_size(h), 1, STRING_UNITS_2, buf, sizeof(buf));
+		pr_warn("HugeTLB: freeing %lu cross-zone hugepage of page size %s failed node%d.\n",
+			freed, buf, nid);
+	}
+
+	return freed;
+}
+
 static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
 {
 	unsigned long i;
@@ -3423,6 +3458,8 @@ static void __init hugetlb_hstate_alloc_pages_onenode(struct hstate *h, int nid)
 		cond_resched();
 	}
 
+	i -= hugetlb_free_cross_zone_pages(h, nid);
+
 	if (!list_empty(&folio_list))
 		prep_and_add_allocated_folios(h, &folio_list);
 
@@ -3496,6 +3533,7 @@ static void __init hugetlb_pages_alloc_boot_node(unsigned long start, unsigned l
 
 static unsigned long __init hugetlb_gigantic_pages_alloc_boot(struct hstate *h)
 {
+	int nid;
 	unsigned long i;
 
 	for (i = 0; i < h->max_huge_pages; ++i) {
@@ -3504,6 +3542,9 @@ static unsigned long __init hugetlb_gigantic_pages_alloc_boot(struct hstate *h)
 		cond_resched();
 	}
 
+	for_each_node(nid)
+		i -= hugetlb_free_cross_zone_pages(h, nid);
+
 	return i;
 }
 
-- 
2.20.1