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.
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Nico Pache <npache@redhat.com>
arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_*
---
include/linux/huge_mm.h | 5 +++++
mm/huge_memory.c | 2 +-
mm/khugepaged.c | 4 ++--
mm/mempolicy.c | 2 +-
mm/page_alloc.c | 2 +-
5 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index a4d9f964dfde..bd7f0e1d8094 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -771,6 +771,11 @@ 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 44ff8a648afd..5eae85818635 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -4097,7 +4097,7 @@ 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 fa1e57fd2c46..c362b3b2e08a 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2000,7 +2000,7 @@ 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)) &&
folio->index == start) {
/* Maybe PMD-mapped */
result = SCAN_PTE_MAPPED_HUGEPAGE;
@@ -2329,7 +2329,7 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned
continue;
}
- if (folio_order(folio) == HPAGE_PMD_ORDER &&
+ if (is_pmd_order(folio_order(folio)) &&
folio->index == start) {
/* Maybe PMD-mapped */
result = SCAN_PTE_MAPPED_HUGEPAGE;
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index dbd48502ac24..3802e52b01fc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2450,7 +2450,7 @@ 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 c2e96ac35636..2acf22f97ae5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -719,7 +719,7 @@ 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;
--
2.53.0On Wed, Feb 11, 2026 at 07:18:32PM -0700, 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. > >Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> >Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> >Signed-off-by: Nico Pache <npache@redhat.com> Reviewed-by: Wei Yang <richard.weiyang@gmail.com> -- Wei Yang Help you, Help me
On 12/02/26 7:48 am, 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.
>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Signed-off-by: Nico Pache <npache@redhat.com>
>
> arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_*
> ---
Thanks, this is useful.
In drivers/dax/device.c and fs/dax.c, we have order == PMD_ORDER check,
not HPAGE_PMD_ORDER. Therefore,
1) Do we have a bug here, in that these codepaths are fault
handlers, therefore should be using HPAGE_PMD_ORDER since the
definition of this macro zeroes out on !CONFIG_PGTABLE_HAS_HUGE_LEAVES?
2) If the distinction between HPAGE_PMD_ORDER and PMD_ORDER is real,
then the helper should be named is_hpage_pmd_order?
> include/linux/huge_mm.h | 5 +++++
> mm/huge_memory.c | 2 +-
> mm/khugepaged.c | 4 ++--
> mm/mempolicy.c | 2 +-
> mm/page_alloc.c | 2 +-
> 5 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index a4d9f964dfde..bd7f0e1d8094 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -771,6 +771,11 @@ 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 44ff8a648afd..5eae85818635 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -4097,7 +4097,7 @@ 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 fa1e57fd2c46..c362b3b2e08a 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2000,7 +2000,7 @@ 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)) &&
> folio->index == start) {
> /* Maybe PMD-mapped */
> result = SCAN_PTE_MAPPED_HUGEPAGE;
> @@ -2329,7 +2329,7 @@ static enum scan_result hpage_collapse_scan_file(struct mm_struct *mm, unsigned
> continue;
> }
>
> - if (folio_order(folio) == HPAGE_PMD_ORDER &&
> + if (is_pmd_order(folio_order(folio)) &&
> folio->index == start) {
> /* Maybe PMD-mapped */
> result = SCAN_PTE_MAPPED_HUGEPAGE;
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index dbd48502ac24..3802e52b01fc 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2450,7 +2450,7 @@ 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 c2e96ac35636..2acf22f97ae5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -719,7 +719,7 @@ 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;
On 2/20/26 11:38, Dev Jain wrote:
>
> On 12/02/26 7:48 am, 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.
>>
>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Signed-off-by: Nico Pache <npache@redhat.com>
>>
>> arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_*
>> ---
>
> Thanks, this is useful.
>
> In drivers/dax/device.c and fs/dax.c, we have order == PMD_ORDER check,
> not HPAGE_PMD_ORDER. Therefore,
>
> 1) Do we have a bug here, in that these codepaths are fault
> handlers, therefore should be using HPAGE_PMD_ORDER since the
> definition of this macro zeroes out on !CONFIG_PGTABLE_HAS_HUGE_LEAVES?
>
> 2) If the distinction between HPAGE_PMD_ORDER and PMD_ORDER is real,
> then the helper should be named is_hpage_pmd_order?
HPAGE_PMD_ORDER is weird a stupid legacy leftover IIUC,
The only thing it checks is that you are not using HPAGE_PMD_ORDER in
code that might be compiled without THP support:
#ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
#define HPAGE_PMD_SHIFT PMD_SHIFT
...
#else
#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })
...
--
Cheers,
David
On 2026/2/12 10:18, 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. > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Signed-off-by: Nico Pache <npache@redhat.com> > > arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_* > --- Looks good to me. Reviewed-by: Lance Yang <lance.yang@linux.dev>
On Thu, Feb 12, 2026 at 10:19 AM Nico Pache <npache@redhat.com> 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. > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Signed-off-by: Nico Pache <npache@redhat.com> LGTM, Reviewed-by: Barry Song <baohua@kernel.org>
On 2/12/26 03:18, 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. > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Signed-off-by: Nico Pache <npache@redhat.com> > > arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_* > --- Acked-by: David Hildenbrand (Arm) <david@kernel.org> -- Cheers, David
On 11 Feb 2026, at 21:18, 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. > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Signed-off-by: Nico Pache <npache@redhat.com> > > arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_* > --- > include/linux/huge_mm.h | 5 +++++ > mm/huge_memory.c | 2 +- > mm/khugepaged.c | 4 ++-- > mm/mempolicy.c | 2 +- > mm/page_alloc.c | 2 +- > 5 files changed, 10 insertions(+), 5 deletions(-) > LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com> Best Regards, Yan, Zi
On Wed, Feb 11, 2026 at 07:18:32PM -0700, 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. > > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> > Signed-off-by: Nico Pache <npache@redhat.com> Reviewed-by: Pedro Falcato <pfalcato@suse.de> > > arches# pick b3ace8be204f # mm/khugepaged: rename hpage_collapse_* to collapse_* ^^Oops? -- Pedro
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