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

Lorenzo Stoakes (Oracle)
2026-03-25T12:11:50Z

On Wed, Mar 25, 2026 at 05:40:19AM -0600, Nico Pache wrote:
> 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>

Nit, but could we please update both to:

Lorenzo Stoakes (Oracle) <ljs@kernel.org>

Thanks :), Lorenzo

> 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
>