[PATCH v2 6/9] mm: page_alloc: add alloc_contig_frozen_pages()

Kefeng Wang
2025-09-02T12:49:34Z

Introduce a ACR_FLAGS_FROZEN flags to indicate that we want to
allocate a frozen compound pages by alloc_contig_range(), also
provide alloc_contig_frozen_pages() to allocate pages without
incrementing their refcount, which may be beneficial to some
users (eg hugetlb).

Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
include/linux/gfp.h | 6 ++++
mm/page_alloc.c | 85 +++++++++++++++++++++++++--------------------
2 files changed, 54 insertions(+), 37 deletions(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 5ebf26fcdcfa..d0047b85fe34 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -427,6 +427,7 @@ extern gfp_t vma_thp_gfp_mask(struct vm_area_struct *vma);
typedef unsigned int __bitwise acr_flags_t;
#define ACR_FLAGS_NONE ((__force acr_flags_t)0) // ordinary allocation request
#define ACR_FLAGS_CMA ((__force acr_flags_t)BIT(0)) // allocate for CMA
+#define ACR_FLAGS_FROZEN ((__force acr_flags_t)BIT(1)) // allocate for frozen compound pages

/* The below functions must be run on a range from a single zone. */
extern int alloc_contig_range_noprof(unsigned long start, unsigned long end,
@@ -437,6 +438,11 @@ extern struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_
int nid, nodemask_t *nodemask);
#define alloc_contig_pages(...) alloc_hooks(alloc_contig_pages_noprof(__VA_ARGS__))

+struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
+ gfp_t gfp_mask, int nid, nodemask_t *nodemask);
+#define alloc_contig_frozen_pages(...) \
+ alloc_hooks(alloc_contig_frozen_pages_noprof(__VA_ARGS__))
+
#endif
void free_contig_range(unsigned long pfn, unsigned long nr_pages);

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index baead29b3e67..0677c49fdff1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6854,6 +6854,9 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
if (__alloc_contig_verify_gfp_mask(gfp_mask, (gfp_t *)&cc.gfp_mask))
return -EINVAL;

+ if ((alloc_flags & ACR_FLAGS_FROZEN) && !(gfp_mask & __GFP_COMP))
+ return -EINVAL;
+
/*
* What we do here is we mark all pageblocks in range as
* MIGRATE_ISOLATE. Because pageblock and max order pages may
@@ -6951,7 +6954,8 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,

check_new_pages(head, order);
prep_new_page(head, order, gfp_mask, 0);
- set_page_refcounted(head);
+ if (!(alloc_flags & ACR_FLAGS_FROZEN))
+ set_page_refcounted(head);
} else {
ret = -EINVAL;
WARN(true, "PFN range: requested [%lu, %lu), allocated [%lu, %lu)\n",
@@ -6963,15 +6967,6 @@ int alloc_contig_range_noprof(unsigned long start, unsigned long end,
}
EXPORT_SYMBOL(alloc_contig_range_noprof);

-static int __alloc_contig_pages(unsigned long start_pfn,
- unsigned long nr_pages, gfp_t gfp_mask)
-{
- unsigned long end_pfn = start_pfn + nr_pages;
-
- return alloc_contig_range_noprof(start_pfn, end_pfn, ACR_FLAGS_NONE,
- gfp_mask);
-}
-
static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
unsigned long nr_pages)
{
@@ -7003,31 +6998,8 @@ static bool zone_spans_last_pfn(const struct zone *zone,
return zone_spans_pfn(zone, last_pfn);
}

-/**
- * alloc_contig_pages() -- tries to find and allocate contiguous range of pages
- * @nr_pages: Number of contiguous pages to allocate
- * @gfp_mask: GFP mask. Node/zone/placement hints limit the search; only some
- * action and reclaim modifiers are supported. Reclaim modifiers
- * control allocation behavior during compaction/migration/reclaim.
- * @nid: Target node
- * @nodemask: Mask for other possible nodes
- *
- * This routine is a wrapper around alloc_contig_range(). It scans over zones
- * on an applicable zonelist to find a contiguous pfn range which can then be
- * tried for allocation with alloc_contig_range(). This routine is intended
- * for allocation requests which can not be fulfilled with the buddy allocator.
- *
- * The allocated memory is always aligned to a page boundary. If nr_pages is a
- * power of two, then allocated range is also guaranteed to be aligned to same
- * nr_pages (e.g. 1GB request would be aligned to 1GB).
- *
- * Allocated pages can be freed with free_contig_range() or by manually calling
- * __free_page() on each allocated page.
- *
- * Return: pointer to contiguous pages on success, or NULL if not successful.
- */
-struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
- int nid, nodemask_t *nodemask)
+static struct page *__alloc_contig_pages(unsigned long nr_pages, gfp_t gfp_mask,
+ acr_flags_t alloc_flags, int nid, nodemask_t *nodemask)
{
unsigned long ret, pfn, flags;
struct zonelist *zonelist;
@@ -7050,8 +7022,8 @@ struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
* and cause alloc_contig_range() to fail...
*/
spin_unlock_irqrestore(&zone->lock, flags);
- ret = __alloc_contig_pages(pfn, nr_pages,
- gfp_mask);
+ ret = alloc_contig_range_noprof(pfn, pfn + nr_pages,
+ alloc_flags, gfp_mask);
if (!ret)
return pfn_to_page(pfn);
spin_lock_irqsave(&zone->lock, flags);
@@ -7062,6 +7034,45 @@ struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
}
return NULL;
}
+
+/**
+ * alloc_contig_pages() -- tries to find and allocate contiguous range of pages
+ * @nr_pages: Number of contiguous pages to allocate
+ * @gfp_mask: GFP mask. Node/zone/placement hints limit the search; only some
+ * action and reclaim modifiers are supported. Reclaim modifiers
+ * control allocation behavior during compaction/migration/reclaim.
+ * @nid: Target node
+ * @nodemask: Mask for other possible nodes
+ *
+ * This routine is a wrapper around alloc_contig_range(). It scans over zones
+ * on an applicable zonelist to find a contiguous pfn range which can then be
+ * tried for allocation with alloc_contig_range(). This routine is intended
+ * for allocation requests which can not be fulfilled with the buddy allocator.
+ *
+ * The allocated memory is always aligned to a page boundary. If nr_pages is a
+ * power of two, then allocated range is also guaranteed to be aligned to same
+ * nr_pages (e.g. 1GB request would be aligned to 1GB).
+ *
+ * Allocated pages can be freed with free_contig_range() or by manually calling
+ * __free_page() on each allocated page.
+ *
+ * Return: pointer to contiguous pages on success, or NULL if not successful.
+ */
+struct page *alloc_contig_pages_noprof(unsigned long nr_pages, gfp_t gfp_mask,
+ int nid, nodemask_t *nodemask)
+{
+ return __alloc_contig_pages(nr_pages, gfp_mask, ACR_FLAGS_NONE,
+ nid, nodemask);
+}
+
+struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages,
+ gfp_t gfp_mask, int nid, nodemask_t *nodemask)
+{
+ /* always allocate compound pages without refcount increased */
+ return __alloc_contig_pages(nr_pages, gfp_mask | __GFP_COMP,
+ ACR_FLAGS_FROZEN, nid, nodemask);
+}
+
#endif /* CONFIG_CONTIG_ALLOC */

void free_contig_range(unsigned long pfn, unsigned long nr_pages)
--
2.27.0