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

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

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
>