From: Lance Yang <lance.yang@linux.dev>
As pointed out by Dev, the PTE checks for disjoint conditions in the
scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn),
and pte_uffd_wp are mutually exclusive.
This patch refactors the loops in both __collapse_huge_page_isolate() and
hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain
instead of separate if blocks.
Also, this is a preparatory step to make it easier to merge the
almost-duplicated scanning logic in these two functions, as suggested
by David.
Suggested-by: Dev Jain <dev.jain@arm.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Lance Yang <lance.yang@linux.dev>
---
mm/khugepaged.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index f4f57ba69d72..808523f92c7b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -548,8 +548,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
_pte++, addr += PAGE_SIZE) {
pte_t pteval = ptep_get(_pte);
- if (pte_none(pteval) || (pte_present(pteval) &&
- is_zero_pfn(pte_pfn(pteval)))) {
+ if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
++none_or_zero;
if (!userfaultfd_armed(vma) &&
(!cc->is_khugepaged ||
@@ -560,12 +559,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
goto out;
}
- }
- if (!pte_present(pteval)) {
+ } else if (!pte_present(pteval)) {
result = SCAN_PTE_NON_PRESENT;
goto out;
- }
- if (pte_uffd_wp(pteval)) {
+ } else if (pte_uffd_wp(pteval)) {
result = SCAN_PTE_UFFD_WP;
goto out;
}
@@ -1316,8 +1313,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
goto out_unmap;
}
- }
- if (pte_uffd_wp(pteval)) {
+ } else if (pte_uffd_wp(pteval)) {
/*
* Don't collapse the page if any of the small
* PTEs are armed with uffd write protection.
--
2.49.0On 2 Oct 2025, at 3:32, Lance Yang wrote: > From: Lance Yang <lance.yang@linux.dev> > > As pointed out by Dev, the PTE checks for disjoint conditions in the > scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn), > and pte_uffd_wp are mutually exclusive. > > This patch refactors the loops in both __collapse_huge_page_isolate() and > hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain > instead of separate if blocks. > > Also, this is a preparatory step to make it easier to merge the > almost-duplicated scanning logic in these two functions, as suggested > by David. > > Suggested-by: Dev Jain <dev.jain@arm.com> > Suggested-by: David Hildenbrand <david@redhat.com> > Signed-off-by: Lance Yang <lance.yang@linux.dev> > --- > mm/khugepaged.c | 12 ++++-------- > 1 file changed, 4 insertions(+), 8 deletions(-) > LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com> Best Regards, Yan, Zi
On 02/10/25 1:02 pm, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> As pointed out by Dev, the PTE checks for disjoint conditions in the
> scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn),
> and pte_uffd_wp are mutually exclusive.
>
> This patch refactors the loops in both __collapse_huge_page_isolate() and
> hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain
> instead of separate if blocks.
>
> Also, this is a preparatory step to make it easier to merge the
> almost-duplicated scanning logic in these two functions, as suggested
> by David.
>
> Suggested-by: Dev Jain <dev.jain@arm.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> ---
> mm/khugepaged.c | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index f4f57ba69d72..808523f92c7b 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -548,8 +548,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> _pte++, addr += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> - if (pte_none(pteval) || (pte_present(pteval) &&
> - is_zero_pfn(pte_pfn(pteval)))) {
> + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
Should have mentioned in the description that pte_present() is not required
here, so removing it.
Reviewed-by: Dev Jain <dev.jain@arm.com>
> ++none_or_zero;
> if (!userfaultfd_armed(vma) &&
> (!cc->is_khugepaged ||
> @@ -560,12 +559,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> goto out;
> }
> - }
> - if (!pte_present(pteval)) {
> + } else if (!pte_present(pteval)) {
> result = SCAN_PTE_NON_PRESENT;
> goto out;
> - }
> - if (pte_uffd_wp(pteval)) {
> + } else if (pte_uffd_wp(pteval)) {
> result = SCAN_PTE_UFFD_WP;
> goto out;
> }
> @@ -1316,8 +1313,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> goto out_unmap;
> }
> - }
> - if (pte_uffd_wp(pteval)) {
> + } else if (pte_uffd_wp(pteval)) {
> /*
> * Don't collapse the page if any of the small
> * PTEs are armed with uffd write protection.
On 2025/10/4 00:33, Dev Jain wrote:
>
> On 02/10/25 1:02 pm, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.dev>
>>
>> As pointed out by Dev, the PTE checks for disjoint conditions in the
>> scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn),
>> and pte_uffd_wp are mutually exclusive.
>>
>> This patch refactors the loops in both __collapse_huge_page_isolate() and
>> hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain
>> instead of separate if blocks.
>>
>> Also, this is a preparatory step to make it easier to merge the
>> almost-duplicated scanning logic in these two functions, as suggested
>> by David.
>>
>> Suggested-by: Dev Jain <dev.jain@arm.com>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Lance Yang <lance.yang@linux.dev>
>> ---
>> mm/khugepaged.c | 12 ++++--------
>> 1 file changed, 4 insertions(+), 8 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index f4f57ba69d72..808523f92c7b 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -548,8 +548,7 @@ static int __collapse_huge_page_isolate(struct
>> vm_area_struct *vma,
>> for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
>> _pte++, addr += PAGE_SIZE) {
>> pte_t pteval = ptep_get(_pte);
>> - if (pte_none(pteval) || (pte_present(pteval) &&
>> - is_zero_pfn(pte_pfn(pteval)))) {
>> + if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
>
> Should have mentioned in the description that pte_present() is not required
> here, so removing it.
Yep, got it.
>
> Reviewed-by: Dev Jain <dev.jain@arm.com>
Cheers,
Lance
>
>> ++none_or_zero;
>> if (!userfaultfd_armed(vma) &&
>> (!cc->is_khugepaged ||
>> @@ -560,12 +559,10 @@ static int __collapse_huge_page_isolate(struct
>> vm_area_struct *vma,
>> count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>> goto out;
>> }
>> - }
>> - if (!pte_present(pteval)) {
>> + } else if (!pte_present(pteval)) {
>> result = SCAN_PTE_NON_PRESENT;
>> goto out;
>> - }
>> - if (pte_uffd_wp(pteval)) {
>> + } else if (pte_uffd_wp(pteval)) {
>> result = SCAN_PTE_UFFD_WP;
>> goto out;
>> }
>> @@ -1316,8 +1313,7 @@ static int hpage_collapse_scan_pmd(struct
>> mm_struct *mm,
>> count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>> goto out_unmap;
>> }
>> - }
>> - if (pte_uffd_wp(pteval)) {
>> + } else if (pte_uffd_wp(pteval)) {
>> /*
>> * Don't collapse the page if any of the small
>> * PTEs are armed with uffd write protection.
On Thu, Oct 02, 2025 at 03:32:54PM +0800, Lance Yang wrote: >From: Lance Yang <lance.yang@linux.dev> > >As pointed out by Dev, the PTE checks for disjoint conditions in the >scanning loops can be optimized. is_swap_pte, (pte_none && is_zero_pfn), >and pte_uffd_wp are mutually exclusive. > >This patch refactors the loops in both __collapse_huge_page_isolate() and >hpage_collapse_scan_pmd() to use a continuous if-else-if-else-if chain >instead of separate if blocks. > >Also, this is a preparatory step to make it easier to merge the >almost-duplicated scanning logic in these two functions, as suggested >by David. > >Suggested-by: Dev Jain <dev.jain@arm.com> >Suggested-by: David Hildenbrand <david@redhat.com> >Signed-off-by: Lance Yang <lance.yang@linux.dev> Reviewed-by: Wei Yang <richard.weiyang@gmail.com> -- Wei Yang Help you, Help me
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