[PATCH mm-unstable v4 2/5] mm: introduce is_pmd_order helper

Nico Pache
2026-03-25T11:41:46Z

In order to add mTHP support to khugepaged, we will often be checking if a
given order is (or is not) a PMD order. Some places in the kernel already
use this check, so lets create a simple helper function to keep the code
clean and readable.

Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Nico Pache <npache@redhat.com>
---
include/linux/huge_mm.h | 5 +++++
mm/huge_memory.c | 2 +-
mm/khugepaged.c | 6 +++---
mm/memory.c | 2 +-
mm/mempolicy.c | 2 +-
mm/page_alloc.c | 4 ++--
mm/shmem.c | 3 +--
7 files changed, 14 insertions(+), 10 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index c8799dca3b60..1258fa37e85b 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -769,6 +769,11 @@ static inline bool pmd_is_huge(pmd_t pmd)
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

+static inline bool is_pmd_order(unsigned int order)
+{
+ return order == HPAGE_PMD_ORDER;
+}
+
static inline int split_folio_to_list_to_order(struct folio *folio,
struct list_head *list, int new_order)
{
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2833b06d7498..b2a6060b3c20 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4118,7 +4118,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order,
i_mmap_unlock_read(mapping);
out:
xas_destroy(&xas);
- if (old_order == HPAGE_PMD_ORDER)
+ if (is_pmd_order(old_order))
count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
count_mthp_stat(old_order, !ret ? MTHP_STAT_SPLIT : MTHP_STAT_SPLIT_FAILED);
return ret;
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6bd7a7c0632a..1f4609761294 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1547,7 +1547,7 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign
if (IS_ERR(folio))
return SCAN_PAGE_NULL;

- if (folio_order(folio) != HPAGE_PMD_ORDER) {
+ if (!is_pmd_order(folio_order(folio))) {
result = SCAN_PAGE_COMPOUND;
goto drop_folio;
}
@@ -2030,7 +2030,7 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
* we locked the first folio, then a THP might be there already.
* This will be discovered on the first iteration.
*/
- if (folio_order(folio) == HPAGE_PMD_ORDER) {
+ if (is_pmd_order(folio_order(folio))) {
result = SCAN_PTE_MAPPED_HUGEPAGE;
goto out_unlock;
}
@@ -2358,7 +2358,7 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm,
continue;
}

- if (folio_order(folio) == HPAGE_PMD_ORDER) {
+ if (is_pmd_order(folio_order(folio))) {
result = SCAN_PTE_MAPPED_HUGEPAGE;
/*
* PMD-sized THP implies that we can only try
diff --git a/mm/memory.c b/mm/memory.c
index 6396d32c348a..e44469f9cf65 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5573,7 +5573,7 @@ vm_fault_t do_set_pmd(struct vm_fault *vmf, struct folio *folio, struct page *pa
if (!thp_vma_suitable_order(vma, haddr, PMD_ORDER))
return ret;

- if (folio_order(folio) != HPAGE_PMD_ORDER)
+ if (!is_pmd_order(folio_order(folio)))
return ret;
page = &folio->page;

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index ff52fb94ff27..fd08771e2057 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2449,7 +2449,7 @@ static struct page *alloc_pages_mpol(gfp_t gfp, unsigned int order,

if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
/* filter "hugepage" allocation, unless from alloc_pages() */
- order == HPAGE_PMD_ORDER && ilx != NO_INTERLEAVE_INDEX) {
+ is_pmd_order(order) && ilx != NO_INTERLEAVE_INDEX) {
/*
* For hugepage allocation and non-interleave policy which
* allows the current node (or other explicitly preferred
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 915b6aef55d0..ee81f5c67c18 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -652,7 +652,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
bool movable;
if (order > PAGE_ALLOC_COSTLY_ORDER) {
- VM_BUG_ON(order != HPAGE_PMD_ORDER);
+ VM_BUG_ON(!is_pmd_order(order));

movable = migratetype == MIGRATE_MOVABLE;

@@ -684,7 +684,7 @@ static inline bool pcp_allowed_order(unsigned int order)
if (order <= PAGE_ALLOC_COSTLY_ORDER)
return true;
#ifdef CONFIG_TRANSPARENT_HUGEPAGE
- if (order == HPAGE_PMD_ORDER)
+ if (is_pmd_order(order))
return true;
#endif
return false;
diff --git a/mm/shmem.c b/mm/shmem.c
index d00044257401..4ecefe02881d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -5532,8 +5532,7 @@ static ssize_t thpsize_shmem_enabled_store(struct kobject *kobj,
spin_unlock(&huge_shmem_orders_lock);
} else if (sysfs_streq(buf, "inherit")) {
/* Do not override huge allocation policy with non-PMD sized mTHP */
- if (shmem_huge == SHMEM_HUGE_FORCE &&
- order != HPAGE_PMD_ORDER)
+ if (shmem_huge == SHMEM_HUGE_FORCE && !is_pmd_order(order))
return -EINVAL;

spin_lock(&huge_shmem_orders_lock);
--
2.53.0