* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-08 4:37 ` [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper Lance Yang
@ 2025-10-09 1:07 ` Andrew Morton
2025-10-09 1:49 ` Lance Yang
2025-10-10 9:10 ` Dev Jain
` (3 subsequent siblings)
4 siblings, 1 reply; 19+ messages in thread
From: Andrew Morton @ 2025-10-09 1:07 UTC (permalink / raw)
To: Lance Yang
Cc: david, lorenzo.stoakes, ziy, baolin.wang, Liam.Howlett, npache,
ryan.roberts, dev.jain, baohua, ioworker0, richard.weiyang,
linux-kernel, linux-mm
On Wed, 8 Oct 2025 12:37:48 +0800 Lance Yang <lance.yang@linux.dev> wrote:
> + if (!cc->is_khugepaged ||
> + *unmapped <= khugepaged_max_ptes_swap) {
> + /*
> + * Always be strict with uffd-wp enabled swap
> + * entries. Please see comment below for
> + * pte_uffd_wp().
> + */
> + if (pte_swp_uffd_wp(pte)) {
> + *scan_result = SCAN_PTE_UFFD_WP;
> + return PTE_CHECK_FAIL;
> + }
> + return PTE_CHECK_CONTINUE;
> + } else {
> + *scan_result = SCAN_EXCEED_SWAP_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> + return PTE_CHECK_FAIL;
> + }
I'm inclined to agree with checkpatch here.
WARNING: else is not generally useful after a break or return
#81: FILE: mm/khugepaged.c:574:
+ return PTE_CHECK_CONTINUE;
+ } else {
did you see this and disagree or did you forget to run checkpatch?
--- a/mm/khugepaged.c~mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper-checkpatch-fixes
+++ a/mm/khugepaged.c
@@ -571,11 +571,10 @@ static inline int thp_collapse_check_pte
(!cc->is_khugepaged ||
*none_or_zero <= khugepaged_max_ptes_none)) {
return PTE_CHECK_CONTINUE;
- } else {
- *scan_result = SCAN_EXCEED_NONE_PTE;
- count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
- return PTE_CHECK_FAIL;
}
+ *scan_result = SCAN_EXCEED_NONE_PTE;
+ count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+ return PTE_CHECK_FAIL;
} else if (!pte_present(pte)) {
if (!unmapped) {
*scan_result = SCAN_PTE_NON_PRESENT;
@@ -600,11 +599,10 @@ static inline int thp_collapse_check_pte
return PTE_CHECK_FAIL;
}
return PTE_CHECK_CONTINUE;
- } else {
- *scan_result = SCAN_EXCEED_SWAP_PTE;
- count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
- return PTE_CHECK_FAIL;
}
+ *scan_result = SCAN_EXCEED_SWAP_PTE;
+ count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
+ return PTE_CHECK_FAIL;
} else if (pte_uffd_wp(pte)) {
/*
* Don't collapse the page if any of the small PTEs are
_
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-09 1:07 ` Andrew Morton
@ 2025-10-09 1:49 ` Lance Yang
0 siblings, 0 replies; 19+ messages in thread
From: Lance Yang @ 2025-10-09 1:49 UTC (permalink / raw)
To: Andrew Morton
Cc: david, lorenzo.stoakes, ziy, baolin.wang, Liam.Howlett, npache,
ryan.roberts, dev.jain, baohua, ioworker0, richard.weiyang,
linux-kernel, linux-mm
On 2025/10/9 09:07, Andrew Morton wrote:
> On Wed, 8 Oct 2025 12:37:48 +0800 Lance Yang <lance.yang@linux.dev> wrote:
>
>> + if (!cc->is_khugepaged ||
>> + *unmapped <= khugepaged_max_ptes_swap) {
>> + /*
>> + * Always be strict with uffd-wp enabled swap
>> + * entries. Please see comment below for
>> + * pte_uffd_wp().
>> + */
>> + if (pte_swp_uffd_wp(pte)) {
>> + *scan_result = SCAN_PTE_UFFD_WP;
>> + return PTE_CHECK_FAIL;
>> + }
>> + return PTE_CHECK_CONTINUE;
>> + } else {
>> + *scan_result = SCAN_EXCEED_SWAP_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>
> I'm inclined to agree with checkpatch here.
Thanks!
>
> WARNING: else is not generally useful after a break or return
> #81: FILE: mm/khugepaged.c:574:
> + return PTE_CHECK_CONTINUE;
> + } else {
>
> did you see this and disagree or did you forget to run checkpatch?
Yes, I saw the warning. I kept the original style because this is just a
code move ...
>
> --- a/mm/khugepaged.c~mm-khugepaged-merge-pte-scanning-logic-into-a-new-helper-checkpatch-fixes
> +++ a/mm/khugepaged.c
> @@ -571,11 +571,10 @@ static inline int thp_collapse_check_pte
> (!cc->is_khugepaged ||
> *none_or_zero <= khugepaged_max_ptes_none)) {
> return PTE_CHECK_CONTINUE;
> - } else {
> - *scan_result = SCAN_EXCEED_NONE_PTE;
> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> - return PTE_CHECK_FAIL;
> }
> + *scan_result = SCAN_EXCEED_NONE_PTE;
> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> + return PTE_CHECK_FAIL;
> } else if (!pte_present(pte)) {
> if (!unmapped) {
> *scan_result = SCAN_PTE_NON_PRESENT;
> @@ -600,11 +599,10 @@ static inline int thp_collapse_check_pte
> return PTE_CHECK_FAIL;
> }
> return PTE_CHECK_CONTINUE;
> - } else {
> - *scan_result = SCAN_EXCEED_SWAP_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> - return PTE_CHECK_FAIL;
> }
> + *scan_result = SCAN_EXCEED_SWAP_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> + return PTE_CHECK_FAIL;
> } else if (pte_uffd_wp(pte)) {
> /*
> * Don't collapse the page if any of the small PTEs are
> _
>
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-08 4:37 ` [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper Lance Yang
2025-10-09 1:07 ` Andrew Morton
@ 2025-10-10 9:10 ` Dev Jain
2025-10-10 10:42 ` Lance Yang
2025-10-10 13:29 ` Wei Yang
` (2 subsequent siblings)
4 siblings, 1 reply; 19+ messages in thread
From: Dev Jain @ 2025-10-10 9:10 UTC (permalink / raw)
To: Lance Yang, akpm, david, lorenzo.stoakes
Cc: ziy, baolin.wang, Liam.Howlett, npache, ryan.roberts, baohua,
ioworker0, richard.weiyang, linux-kernel, linux-mm
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On 08/10/25 10:07 am, Lance Yang wrote:
> }
> }
>
> +/*
> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
> + * @pte: The PTE to check
> + * @vma: The VMA the PTE belongs to
> + * @addr: The virtual address corresponding to this PTE
> + * @foliop: On success, used to return a pointer to the folio
> + * Must be non-NULL
> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
> + * @shared: Counter for shared pages. Must be non-NULL
> + * @scan_result: Used to return the failure reason (SCAN_*) on a
> + * PTE_CHECK_FAIL return. Must be non-NULL
> + * @cc: Collapse control settings
> + *
> + * Returns:
> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
> + * PTE_CHECK_FAIL - Abort collapse scan
> + */
> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
> + unsigned long addr, struct folio **foliop, int *none_or_zero,
> + int *unmapped, int *shared, int *scan_result,
> + struct collapse_control *cc)
> +{
> + struct folio *folio = NULL;
I think initialization is not needed here?Otherwise, LGTM. Reviewed-by: Dev Jain <dev.jain@arm.com>
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^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-10 9:10 ` Dev Jain
@ 2025-10-10 10:42 ` Lance Yang
0 siblings, 0 replies; 19+ messages in thread
From: Lance Yang @ 2025-10-10 10:42 UTC (permalink / raw)
To: Dev Jain
Cc: ziy, baolin.wang, Liam.Howlett, npache, ryan.roberts, baohua,
ioworker0, david, richard.weiyang, lorenzo.stoakes, linux-kernel,
akpm, linux-mm
On 2025/10/10 17:10, Dev Jain wrote:
>
> On 08/10/25 10:07 am, Lance Yang wrote:
>> }
>> }
>>
>> +/*
>> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
>> + * @pte: The PTE to check
>> + * @vma: The VMA the PTE belongs to
>> + * @addr: The virtual address corresponding to this PTE
>> + * @foliop: On success, used to return a pointer to the folio
>> + * Must be non-NULL
>> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
>> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
>> + * @shared: Counter for shared pages. Must be non-NULL
>> + * @scan_result: Used to return the failure reason (SCAN_*) on a
>> + * PTE_CHECK_FAIL return. Must be non-NULL
>> + * @cc: Collapse control settings
>> + *
>> + * Returns:
>> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
>> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
>> + * PTE_CHECK_FAIL - Abort collapse scan
>> + */
>> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
>> + unsigned long addr, struct folio **foliop, int *none_or_zero,
>> + int *unmapped, int *shared, int *scan_result,
>> + struct collapse_control *cc)
>> +{
>> + struct folio *folio = NULL;
>
> I think initialization is not needed here?Otherwise, LGTM. Reviewed-by: Dev Jain <dev.jain@arm.com>
Yep. It's a minor thing, so I'll fold that in if a new version is
needed. Thanks!
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-08 4:37 ` [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper Lance Yang
2025-10-09 1:07 ` Andrew Morton
2025-10-10 9:10 ` Dev Jain
@ 2025-10-10 13:29 ` Wei Yang
2025-10-10 13:55 ` Lance Yang
2025-10-14 12:36 ` Lorenzo Stoakes
2025-10-14 17:41 ` Lorenzo Stoakes
4 siblings, 1 reply; 19+ messages in thread
From: Wei Yang @ 2025-10-10 13:29 UTC (permalink / raw)
To: Lance Yang
Cc: akpm, david, lorenzo.stoakes, ziy, baolin.wang, Liam.Howlett,
npache, ryan.roberts, dev.jain, baohua, ioworker0,
richard.weiyang, linux-kernel, linux-mm
On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote:
>From: Lance Yang <lance.yang@linux.dev>
>
>As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
>and __collapse_huge_page_isolate() was almost duplicated.
>
>This patch cleans things up by moving all the common PTE checking logic
>into a new shared helper, thp_collapse_check_pte(). While at it, we use
>vm_normal_folio() instead of vm_normal_page().
>
>Suggested-by: David Hildenbrand <david@redhat.com>
>Suggested-by: Dev Jain <dev.jain@arm.com>
>Signed-off-by: Lance Yang <lance.yang@linux.dev>
>---
> mm/khugepaged.c | 243 ++++++++++++++++++++++++++----------------------
> 1 file changed, 130 insertions(+), 113 deletions(-)
>
>diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>index b5c0295c3414..7116caae1fa4 100644
>--- a/mm/khugepaged.c
>+++ b/mm/khugepaged.c
>@@ -61,6 +61,12 @@ enum scan_result {
> SCAN_PAGE_FILLED,
> };
>
>+enum pte_check_result {
>+ PTE_CHECK_SUCCEED,
>+ PTE_CHECK_CONTINUE,
>+ PTE_CHECK_FAIL,
>+};
>+
> #define CREATE_TRACE_POINTS
> #include <trace/events/huge_memory.h>
>
>@@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
> }
> }
>
>+/*
>+ * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
>+ * @pte: The PTE to check
>+ * @vma: The VMA the PTE belongs to
>+ * @addr: The virtual address corresponding to this PTE
>+ * @foliop: On success, used to return a pointer to the folio
>+ * Must be non-NULL
>+ * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
>+ * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
>+ * @shared: Counter for shared pages. Must be non-NULL
>+ * @scan_result: Used to return the failure reason (SCAN_*) on a
>+ * PTE_CHECK_FAIL return. Must be non-NULL
>+ * @cc: Collapse control settings
>+ *
>+ * Returns:
>+ * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
>+ * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
>+ * PTE_CHECK_FAIL - Abort collapse scan
>+ */
>+static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
>+ unsigned long addr, struct folio **foliop, int *none_or_zero,
>+ int *unmapped, int *shared, int *scan_result,
>+ struct collapse_control *cc)
>+{
>+ struct folio *folio = NULL;
>+
>+ if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
>+ (*none_or_zero)++;
>+ if (!userfaultfd_armed(vma) &&
>+ (!cc->is_khugepaged ||
>+ *none_or_zero <= khugepaged_max_ptes_none)) {
>+ return PTE_CHECK_CONTINUE;
>+ } else {
>+ *scan_result = SCAN_EXCEED_NONE_PTE;
>+ count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>+ return PTE_CHECK_FAIL;
>+ }
>+ } else if (!pte_present(pte)) {
>+ if (!unmapped) {
>+ *scan_result = SCAN_PTE_NON_PRESENT;
>+ return PTE_CHECK_FAIL;
>+ }
>+
>+ if (non_swap_entry(pte_to_swp_entry(pte))) {
>+ *scan_result = SCAN_PTE_NON_PRESENT;
>+ return PTE_CHECK_FAIL;
>+ }
>+
>+ (*unmapped)++;
>+ if (!cc->is_khugepaged ||
>+ *unmapped <= khugepaged_max_ptes_swap) {
>+ /*
>+ * Always be strict with uffd-wp enabled swap
>+ * entries. Please see comment below for
>+ * pte_uffd_wp().
>+ */
>+ if (pte_swp_uffd_wp(pte)) {
>+ *scan_result = SCAN_PTE_UFFD_WP;
>+ return PTE_CHECK_FAIL;
>+ }
>+ return PTE_CHECK_CONTINUE;
>+ } else {
>+ *scan_result = SCAN_EXCEED_SWAP_PTE;
>+ count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>+ return PTE_CHECK_FAIL;
>+ }
>+ } else if (pte_uffd_wp(pte)) {
>+ /*
>+ * Don't collapse the page if any of the small PTEs are
>+ * armed with uffd write protection. Here we can also mark
>+ * the new huge pmd as write protected if any of the small
>+ * ones is marked but that could bring unknown userfault
>+ * messages that falls outside of the registered range.
>+ * So, just be simple.
>+ */
>+ *scan_result = SCAN_PTE_UFFD_WP;
>+ return PTE_CHECK_FAIL;
>+ }
>+
>+ folio = vm_normal_folio(vma, addr, pte);
>+ if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
>+ *scan_result = SCAN_PAGE_NULL;
>+ return PTE_CHECK_FAIL;
>+ }
>+
>+ if (!folio_test_anon(folio)) {
>+ VM_WARN_ON_FOLIO(true, folio);
>+ *scan_result = SCAN_PAGE_ANON;
>+ return PTE_CHECK_FAIL;
>+ }
>+
>+ /*
>+ * We treat a single page as shared if any part of the THP
>+ * is shared.
>+ */
>+ if (folio_maybe_mapped_shared(folio)) {
>+ (*shared)++;
>+ if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
>+ *scan_result = SCAN_EXCEED_SHARED_PTE;
>+ count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
>+ return PTE_CHECK_FAIL;
>+ }
>+ }
>+
>+ *foliop = folio;
>+
>+ return PTE_CHECK_SUCCEED;
>+}
>+
This one looks much better.
While my personal feeling is this is not a complete work to merge the scanning
logic. We still have folio_expected_ref_count() and pte_young() check present
both in __collapse_huge_page_isolate() and huge_collapse_scan_pmd().
--
Wei Yang
Help you, Help me
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-10 13:29 ` Wei Yang
@ 2025-10-10 13:55 ` Lance Yang
0 siblings, 0 replies; 19+ messages in thread
From: Lance Yang @ 2025-10-10 13:55 UTC (permalink / raw)
To: Wei Yang
Cc: akpm, david, lorenzo.stoakes, ziy, baolin.wang, Liam.Howlett,
npache, ryan.roberts, dev.jain, baohua, ioworker0, linux-kernel,
linux-mm
On 2025/10/10 21:29, Wei Yang wrote:
> On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.dev>
>>
>> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
>> and __collapse_huge_page_isolate() was almost duplicated.
>>
>> This patch cleans things up by moving all the common PTE checking logic
>> into a new shared helper, thp_collapse_check_pte(). While at it, we use
>> vm_normal_folio() instead of vm_normal_page().
>>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Suggested-by: Dev Jain <dev.jain@arm.com>
>> Signed-off-by: Lance Yang <lance.yang@linux.dev>
>> ---
>> mm/khugepaged.c | 243 ++++++++++++++++++++++++++----------------------
>> 1 file changed, 130 insertions(+), 113 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index b5c0295c3414..7116caae1fa4 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -61,6 +61,12 @@ enum scan_result {
>> SCAN_PAGE_FILLED,
>> };
>>
>> +enum pte_check_result {
>> + PTE_CHECK_SUCCEED,
>> + PTE_CHECK_CONTINUE,
>> + PTE_CHECK_FAIL,
>> +};
>> +
>> #define CREATE_TRACE_POINTS
>> #include <trace/events/huge_memory.h>
>>
>> @@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
>> }
>> }
>>
>> +/*
>> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
>> + * @pte: The PTE to check
>> + * @vma: The VMA the PTE belongs to
>> + * @addr: The virtual address corresponding to this PTE
>> + * @foliop: On success, used to return a pointer to the folio
>> + * Must be non-NULL
>> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
>> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
>> + * @shared: Counter for shared pages. Must be non-NULL
>> + * @scan_result: Used to return the failure reason (SCAN_*) on a
>> + * PTE_CHECK_FAIL return. Must be non-NULL
>> + * @cc: Collapse control settings
>> + *
>> + * Returns:
>> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
>> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
>> + * PTE_CHECK_FAIL - Abort collapse scan
>> + */
>> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
>> + unsigned long addr, struct folio **foliop, int *none_or_zero,
>> + int *unmapped, int *shared, int *scan_result,
>> + struct collapse_control *cc)
>> +{
>> + struct folio *folio = NULL;
>> +
>> + if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
>> + (*none_or_zero)++;
>> + if (!userfaultfd_armed(vma) &&
>> + (!cc->is_khugepaged ||
>> + *none_or_zero <= khugepaged_max_ptes_none)) {
>> + return PTE_CHECK_CONTINUE;
>> + } else {
>> + *scan_result = SCAN_EXCEED_NONE_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + } else if (!pte_present(pte)) {
>> + if (!unmapped) {
>> + *scan_result = SCAN_PTE_NON_PRESENT;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + if (non_swap_entry(pte_to_swp_entry(pte))) {
>> + *scan_result = SCAN_PTE_NON_PRESENT;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + (*unmapped)++;
>> + if (!cc->is_khugepaged ||
>> + *unmapped <= khugepaged_max_ptes_swap) {
>> + /*
>> + * Always be strict with uffd-wp enabled swap
>> + * entries. Please see comment below for
>> + * pte_uffd_wp().
>> + */
>> + if (pte_swp_uffd_wp(pte)) {
>> + *scan_result = SCAN_PTE_UFFD_WP;
>> + return PTE_CHECK_FAIL;
>> + }
>> + return PTE_CHECK_CONTINUE;
>> + } else {
>> + *scan_result = SCAN_EXCEED_SWAP_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + } else if (pte_uffd_wp(pte)) {
>> + /*
>> + * Don't collapse the page if any of the small PTEs are
>> + * armed with uffd write protection. Here we can also mark
>> + * the new huge pmd as write protected if any of the small
>> + * ones is marked but that could bring unknown userfault
>> + * messages that falls outside of the registered range.
>> + * So, just be simple.
>> + */
>> + *scan_result = SCAN_PTE_UFFD_WP;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + folio = vm_normal_folio(vma, addr, pte);
>> + if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
>> + *scan_result = SCAN_PAGE_NULL;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + if (!folio_test_anon(folio)) {
>> + VM_WARN_ON_FOLIO(true, folio);
>> + *scan_result = SCAN_PAGE_ANON;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + /*
>> + * We treat a single page as shared if any part of the THP
>> + * is shared.
>> + */
>> + if (folio_maybe_mapped_shared(folio)) {
>> + (*shared)++;
>> + if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
>> + *scan_result = SCAN_EXCEED_SHARED_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + }
>> +
>> + *foliop = folio;
>> +
>> + return PTE_CHECK_SUCCEED;
>> +}
>> +
>
> This one looks much better.
>
> While my personal feeling is this is not a complete work to merge the scanning
> logic. We still have folio_expected_ref_count() and pte_young() check present
> both in __collapse_huge_page_isolate() and huge_collapse_scan_pmd().
Yep, good catch!
There's definitely more that can be done. For now, let's keep this patch
as-is to avoid making it too complex. Let's get this one in first, and
then we can work on the next step :)
^ permalink raw reply [flat|nested] 19+ messages in thread
* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-08 4:37 ` [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper Lance Yang
` (2 preceding siblings ...)
2025-10-10 13:29 ` Wei Yang
@ 2025-10-14 12:36 ` Lorenzo Stoakes
2025-10-14 17:41 ` Lorenzo Stoakes
4 siblings, 0 replies; 19+ messages in thread
From: Lorenzo Stoakes @ 2025-10-14 12:36 UTC (permalink / raw)
To: Lance Yang
Cc: akpm, david, ziy, baolin.wang, Liam.Howlett, npache,
ryan.roberts, dev.jain, baohua, ioworker0, richard.weiyang,
linux-kernel, linux-mm
On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
> and __collapse_huge_page_isolate() was almost duplicated.
>
> This patch cleans things up by moving all the common PTE checking logic
> into a new shared helper, thp_collapse_check_pte(). While at it, we use
> vm_normal_folio() instead of vm_normal_page().
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
In general I like the idea, the implementation needs work though.
Will check in more detail on respin
> ---
> mm/khugepaged.c | 243 ++++++++++++++++++++++++++----------------------
> 1 file changed, 130 insertions(+), 113 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b5c0295c3414..7116caae1fa4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -61,6 +61,12 @@ enum scan_result {
> SCAN_PAGE_FILLED,
> };
>
> +enum pte_check_result {
> + PTE_CHECK_SUCCEED,
> + PTE_CHECK_CONTINUE,
Don't love this logic - this feels like we're essentially abstracting
control flow, I mean what does 'continue' mean here? Other than you're in a
loop and please continue, which is relying a little too much on what the
caller does.
if we retain this logic something like PTE_CHECK_SKIP would make more sense.
> + PTE_CHECK_FAIL,
> +};
> +
> #define CREATE_TRACE_POINTS
> #include <trace/events/huge_memory.h>
>
> @@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
> }
> }
>
> +/*
> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
> + * @pte: The PTE to check
> + * @vma: The VMA the PTE belongs to
> + * @addr: The virtual address corresponding to this PTE
> + * @foliop: On success, used to return a pointer to the folio
> + * Must be non-NULL
> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
> + * @shared: Counter for shared pages. Must be non-NULL
> + * @scan_result: Used to return the failure reason (SCAN_*) on a
> + * PTE_CHECK_FAIL return. Must be non-NULL
> + * @cc: Collapse control settings
Do we really need this many parameters? THis is hard to follow.
Of course it being me, I'd immediately prefer a helper struct :)
> + *
> + * Returns:
> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
> + * PTE_CHECK_FAIL - Abort collapse scan
> + */
> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
There's no need for inline in an internal static function in a file.
> + unsigned long addr, struct folio **foliop, int *none_or_zero,
> + int *unmapped, int *shared, int *scan_result,
> + struct collapse_control *cc)
> +{
> + struct folio *folio = NULL;
> +
> + if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
> + (*none_or_zero)++;
> + if (!userfaultfd_armed(vma) &&
> + (!cc->is_khugepaged ||
> + *none_or_zero <= khugepaged_max_ptes_none)) {
> + return PTE_CHECK_CONTINUE;
> + } else {
> + *scan_result = SCAN_EXCEED_NONE_PTE;
> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + } else if (!pte_present(pte)) {
You're now making the if-else issues with previous patches worse by
returning which gets even checkpatch to warn you.
if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
(of course note that I am not convinced you can drop the pte_present()
check here)
(*none_or_zero)++;
if (!userfaultfd_armed(vma) &&
(!cc->is_khugepaged ||
*none_or_zero <= khugepaged_max_ptes_none))
return PTE_CHECK_CONTINUE;
*scan_result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
return PTE_CHECK_FAIL;
}
if (!pte_present(pte)) {
...
}
But even that really needs seriously more refactoring - that condition
above is horrible for instance so, e.g.:
if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
(*none_or_zero)++;
/* Cases where this is acceptable. */
if (!userfaultfd_armed(vma))
return PTE_CHECK_SKIP;
if (!cc->is_khugepaged)
return PTE_CHECK_SKIP;
if (*none_or_zero <= khugepaged_max_ptes_none)
return PTE_CHECK_SKIP;
/* Otherwise, we must abort the scan. */
*scan_result = SCAN_EXCEED_NONE_PTE;
count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
return PTE_CHECK_FAIL;
}
if (!pte_present(pte)) {
...
}
Improves things a lot.
I do however _hate_ this (*blah)++; thing. A helper struct would help :)
> + if (!unmapped) {
> + *scan_result = SCAN_PTE_NON_PRESENT;
> + return PTE_CHECK_FAIL;
Can't we have a helper that sets the result, e.g.:
return pte_check_fail(scan_result, SCAN_PTE_NON_PRESENT);
static enum pte_check_result pte_check_fail(int *scan_result,
enum pte_check_result result)
{
*scan_result = result;
return PTE_CHECK_FAIL;
}
And same for success/skip
Then all of these horrible if (blah) { *foo = bar; return baz; } can be
made into
if (blah)
return pte_check_xxx(..., SCAN_PTE_...);
> + }
> +
> + if (non_swap_entry(pte_to_swp_entry(pte))) {
> + *scan_result = SCAN_PTE_NON_PRESENT;
> + return PTE_CHECK_FAIL;
> + }
> +
> + (*unmapped)++;
> + if (!cc->is_khugepaged ||
> + *unmapped <= khugepaged_max_ptes_swap) {
> + /*
> + * Always be strict with uffd-wp enabled swap
> + * entries. Please see comment below for
> + * pte_uffd_wp().
> + */
> + if (pte_swp_uffd_wp(pte)) {
> + *scan_result = SCAN_PTE_UFFD_WP;
> + return PTE_CHECK_FAIL;
> + }
> + return PTE_CHECK_CONTINUE;
> + } else {
> + *scan_result = SCAN_EXCEED_SWAP_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + } else if (pte_uffd_wp(pte)) {
> + /*
> + * Don't collapse the page if any of the small PTEs are
> + * armed with uffd write protection. Here we can also mark
> + * the new huge pmd as write protected if any of the small
> + * ones is marked but that could bring unknown userfault
> + * messages that falls outside of the registered range.
> + * So, just be simple.
> + */
> + *scan_result = SCAN_PTE_UFFD_WP;
> + return PTE_CHECK_FAIL;
> + }
> +
Again as all of the comments for previous series still apply here so
obviously I don't like this as-is :)
And as Andrew has pointed out, now checkpatch is finding the 'pointless
else' issue (as mentioned above also).
> + folio = vm_normal_folio(vma, addr, pte);
> + if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
> + *scan_result = SCAN_PAGE_NULL;
> + return PTE_CHECK_FAIL;
> + }
> +
> + if (!folio_test_anon(folio)) {
> + VM_WARN_ON_FOLIO(true, folio);
> + *scan_result = SCAN_PAGE_ANON;
> + return PTE_CHECK_FAIL;
> + }
> +
> + /*
> + * We treat a single page as shared if any part of the THP
> + * is shared.
> + */
> + if (folio_maybe_mapped_shared(folio)) {
> + (*shared)++;
> + if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
> + *scan_result = SCAN_EXCEED_SHARED_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + }
> +
> + *foliop = folio;
> +
> + return PTE_CHECK_SUCCEED;
> +}
> +
> static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> unsigned long start_addr,
> pte_t *pte,
> struct collapse_control *cc,
> struct list_head *compound_pagelist)
> {
> - struct page *page = NULL;
> struct folio *folio = NULL;
> unsigned long addr = start_addr;
> pte_t *_pte;
> int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
> + int pte_check_res;
>
> for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> _pte++, addr += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> - ++none_or_zero;
> - if (!userfaultfd_armed(vma) &&
> - (!cc->is_khugepaged ||
> - none_or_zero <= khugepaged_max_ptes_none)) {
> - continue;
> - } else {
> - result = SCAN_EXCEED_NONE_PTE;
> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> - goto out;
> - }
> - } else if (!pte_present(pteval)) {
> - result = SCAN_PTE_NON_PRESENT;
> - goto out;
> - } else if (pte_uffd_wp(pteval)) {
> - result = SCAN_PTE_UFFD_WP;
> - goto out;
> - }
> - page = vm_normal_page(vma, addr, pteval);
> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> - result = SCAN_PAGE_NULL;
> - goto out;
> - }
>
> - folio = page_folio(page);
> - if (!folio_test_anon(folio)) {
> - VM_WARN_ON_FOLIO(true, folio);
> - result = SCAN_PAGE_ANON;
> - goto out;
> - }
> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
> + &folio, &none_or_zero, NULL, &shared,
> + &result, cc);
>
> - /* See hpage_collapse_scan_pmd(). */
> - if (folio_maybe_mapped_shared(folio)) {
> - ++shared;
> - if (cc->is_khugepaged &&
> - shared > khugepaged_max_ptes_shared) {
> - result = SCAN_EXCEED_SHARED_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> - goto out;
> - }
> - }
> + if (pte_check_res == PTE_CHECK_CONTINUE)
> + continue;
> + else if (pte_check_res == PTE_CHECK_FAIL)
> + goto out;
>
> if (folio_test_large(folio)) {
> struct folio *f;
> @@ -1264,11 +1347,11 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> pte_t *pte, *_pte;
> int result = SCAN_FAIL, referenced = 0;
> int none_or_zero = 0, shared = 0;
> - struct page *page = NULL;
> struct folio *folio = NULL;
> unsigned long addr;
> spinlock_t *ptl;
> int node = NUMA_NO_NODE, unmapped = 0;
> + int pte_check_res;
>
> VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK);
>
> @@ -1287,81 +1370,15 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR;
> _pte++, addr += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> - ++none_or_zero;
> - if (!userfaultfd_armed(vma) &&
> - (!cc->is_khugepaged ||
> - none_or_zero <= khugepaged_max_ptes_none)) {
> - continue;
> - } else {
> - result = SCAN_EXCEED_NONE_PTE;
> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> - goto out_unmap;
> - }
> - } else if (!pte_present(pteval)) {
> - if (non_swap_entry(pte_to_swp_entry(pteval))) {
> - result = SCAN_PTE_NON_PRESENT;
> - goto out_unmap;
> - }
>
> - ++unmapped;
> - if (!cc->is_khugepaged ||
> - unmapped <= khugepaged_max_ptes_swap) {
> - /*
> - * Always be strict with uffd-wp
> - * enabled swap entries. Please see
> - * comment below for pte_uffd_wp().
> - */
> - if (pte_swp_uffd_wp(pteval)) {
> - result = SCAN_PTE_UFFD_WP;
> - goto out_unmap;
> - }
> - continue;
> - } else {
> - result = SCAN_EXCEED_SWAP_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> - goto out_unmap;
> - }
> - } else if (pte_uffd_wp(pteval)) {
> - /*
> - * Don't collapse the page if any of the small
> - * PTEs are armed with uffd write protection.
> - * Here we can also mark the new huge pmd as
> - * write protected if any of the small ones is
> - * marked but that could bring unknown
> - * userfault messages that falls outside of
> - * the registered range. So, just be simple.
> - */
> - result = SCAN_PTE_UFFD_WP;
> - goto out_unmap;
> - }
> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
> + &folio, &none_or_zero, &unmapped,
> + &shared, &result, cc);
>
> - page = vm_normal_page(vma, addr, pteval);
> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> - result = SCAN_PAGE_NULL;
> - goto out_unmap;
> - }
> - folio = page_folio(page);
> -
> - if (!folio_test_anon(folio)) {
> - VM_WARN_ON_FOLIO(true, folio);
> - result = SCAN_PAGE_ANON;
> + if (pte_check_res == PTE_CHECK_CONTINUE)
> + continue;
> + else if (pte_check_res == PTE_CHECK_FAIL)
> goto out_unmap;
> - }
> -
> - /*
> - * We treat a single page as shared if any part of the THP
> - * is shared.
> - */
> - if (folio_maybe_mapped_shared(folio)) {
> - ++shared;
> - if (cc->is_khugepaged &&
> - shared > khugepaged_max_ptes_shared) {
> - result = SCAN_EXCEED_SHARED_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> - goto out_unmap;
> - }
> - }
>
> /*
> * Record which node the original page is from and save this
> --
> 2.49.0
>
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-08 4:37 ` [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper Lance Yang
` (3 preceding siblings ...)
2025-10-14 12:36 ` Lorenzo Stoakes
@ 2025-10-14 17:41 ` Lorenzo Stoakes
2025-10-15 1:48 ` Lance Yang
4 siblings, 1 reply; 19+ messages in thread
From: Lorenzo Stoakes @ 2025-10-14 17:41 UTC (permalink / raw)
To: Lance Yang
Cc: akpm, david, ziy, baolin.wang, Liam.Howlett, npache,
ryan.roberts, dev.jain, baohua, ioworker0, richard.weiyang,
linux-kernel, linux-mm
OK so this patch _is_ based on [0] already being applied then?
I don't see any is_swap_pte() here so presumably so right?
Can we just respin these series and put them together? Because now I've
reviewed a bunch of stuff in [0], which this series depends upon, and
you're saying we should now review on this instead of that and it's a bit
of a mess.
Once review here is dealt with can you combine [0] into this series please?
For [0] I would like you to reinstate the is_swap_pte() conditional as
(copiously :) discussed over there.
[0}: https://lore.kernel.org/all/20251008032657.72406-1-lance.yang@linux.dev/
Thanks, Lorenzo
On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote:
> From: Lance Yang <lance.yang@linux.dev>
>
> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
> and __collapse_huge_page_isolate() was almost duplicated.
>
> This patch cleans things up by moving all the common PTE checking logic
> into a new shared helper, thp_collapse_check_pte(). While at it, we use
> vm_normal_folio() instead of vm_normal_page().
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Dev Jain <dev.jain@arm.com>
> Signed-off-by: Lance Yang <lance.yang@linux.dev>
> ---
> mm/khugepaged.c | 243 ++++++++++++++++++++++++++----------------------
> 1 file changed, 130 insertions(+), 113 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b5c0295c3414..7116caae1fa4 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -61,6 +61,12 @@ enum scan_result {
> SCAN_PAGE_FILLED,
> };
>
> +enum pte_check_result {
> + PTE_CHECK_SUCCEED,
> + PTE_CHECK_CONTINUE,
> + PTE_CHECK_FAIL,
> +};
> +
> #define CREATE_TRACE_POINTS
> #include <trace/events/huge_memory.h>
>
> @@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
> }
> }
>
> +/*
> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
> + * @pte: The PTE to check
> + * @vma: The VMA the PTE belongs to
> + * @addr: The virtual address corresponding to this PTE
> + * @foliop: On success, used to return a pointer to the folio
> + * Must be non-NULL
> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
> + * @shared: Counter for shared pages. Must be non-NULL
> + * @scan_result: Used to return the failure reason (SCAN_*) on a
> + * PTE_CHECK_FAIL return. Must be non-NULL
> + * @cc: Collapse control settings
> + *
> + * Returns:
> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
> + * PTE_CHECK_FAIL - Abort collapse scan
> + */
> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
> + unsigned long addr, struct folio **foliop, int *none_or_zero,
> + int *unmapped, int *shared, int *scan_result,
> + struct collapse_control *cc)
> +{
> + struct folio *folio = NULL;
> +
> + if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
> + (*none_or_zero)++;
> + if (!userfaultfd_armed(vma) &&
> + (!cc->is_khugepaged ||
> + *none_or_zero <= khugepaged_max_ptes_none)) {
> + return PTE_CHECK_CONTINUE;
> + } else {
> + *scan_result = SCAN_EXCEED_NONE_PTE;
> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + } else if (!pte_present(pte)) {
> + if (!unmapped) {
> + *scan_result = SCAN_PTE_NON_PRESENT;
> + return PTE_CHECK_FAIL;
> + }
> +
> + if (non_swap_entry(pte_to_swp_entry(pte))) {
> + *scan_result = SCAN_PTE_NON_PRESENT;
> + return PTE_CHECK_FAIL;
> + }
> +
> + (*unmapped)++;
> + if (!cc->is_khugepaged ||
> + *unmapped <= khugepaged_max_ptes_swap) {
> + /*
> + * Always be strict with uffd-wp enabled swap
> + * entries. Please see comment below for
> + * pte_uffd_wp().
> + */
> + if (pte_swp_uffd_wp(pte)) {
> + *scan_result = SCAN_PTE_UFFD_WP;
> + return PTE_CHECK_FAIL;
> + }
> + return PTE_CHECK_CONTINUE;
> + } else {
> + *scan_result = SCAN_EXCEED_SWAP_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + } else if (pte_uffd_wp(pte)) {
> + /*
> + * Don't collapse the page if any of the small PTEs are
> + * armed with uffd write protection. Here we can also mark
> + * the new huge pmd as write protected if any of the small
> + * ones is marked but that could bring unknown userfault
> + * messages that falls outside of the registered range.
> + * So, just be simple.
> + */
> + *scan_result = SCAN_PTE_UFFD_WP;
> + return PTE_CHECK_FAIL;
> + }
> +
> + folio = vm_normal_folio(vma, addr, pte);
> + if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
> + *scan_result = SCAN_PAGE_NULL;
> + return PTE_CHECK_FAIL;
> + }
> +
> + if (!folio_test_anon(folio)) {
> + VM_WARN_ON_FOLIO(true, folio);
> + *scan_result = SCAN_PAGE_ANON;
> + return PTE_CHECK_FAIL;
> + }
> +
> + /*
> + * We treat a single page as shared if any part of the THP
> + * is shared.
> + */
> + if (folio_maybe_mapped_shared(folio)) {
> + (*shared)++;
> + if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
> + *scan_result = SCAN_EXCEED_SHARED_PTE;
> + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> + return PTE_CHECK_FAIL;
> + }
> + }
> +
> + *foliop = folio;
> +
> + return PTE_CHECK_SUCCEED;
> +}
> +
> static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
> unsigned long start_addr,
> pte_t *pte,
> struct collapse_control *cc,
> struct list_head *compound_pagelist)
> {
> - struct page *page = NULL;
> struct folio *folio = NULL;
> unsigned long addr = start_addr;
> pte_t *_pte;
> int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
> + int pte_check_res;
>
> for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
> _pte++, addr += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> - ++none_or_zero;
> - if (!userfaultfd_armed(vma) &&
> - (!cc->is_khugepaged ||
> - none_or_zero <= khugepaged_max_ptes_none)) {
> - continue;
> - } else {
> - result = SCAN_EXCEED_NONE_PTE;
> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> - goto out;
> - }
> - } else if (!pte_present(pteval)) {
> - result = SCAN_PTE_NON_PRESENT;
> - goto out;
> - } else if (pte_uffd_wp(pteval)) {
> - result = SCAN_PTE_UFFD_WP;
> - goto out;
> - }
> - page = vm_normal_page(vma, addr, pteval);
> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> - result = SCAN_PAGE_NULL;
> - goto out;
> - }
>
> - folio = page_folio(page);
> - if (!folio_test_anon(folio)) {
> - VM_WARN_ON_FOLIO(true, folio);
> - result = SCAN_PAGE_ANON;
> - goto out;
> - }
> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
> + &folio, &none_or_zero, NULL, &shared,
> + &result, cc);
>
> - /* See hpage_collapse_scan_pmd(). */
> - if (folio_maybe_mapped_shared(folio)) {
> - ++shared;
> - if (cc->is_khugepaged &&
> - shared > khugepaged_max_ptes_shared) {
> - result = SCAN_EXCEED_SHARED_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> - goto out;
> - }
> - }
> + if (pte_check_res == PTE_CHECK_CONTINUE)
> + continue;
> + else if (pte_check_res == PTE_CHECK_FAIL)
> + goto out;
>
> if (folio_test_large(folio)) {
> struct folio *f;
> @@ -1264,11 +1347,11 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> pte_t *pte, *_pte;
> int result = SCAN_FAIL, referenced = 0;
> int none_or_zero = 0, shared = 0;
> - struct page *page = NULL;
> struct folio *folio = NULL;
> unsigned long addr;
> spinlock_t *ptl;
> int node = NUMA_NO_NODE, unmapped = 0;
> + int pte_check_res;
>
> VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK);
>
> @@ -1287,81 +1370,15 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
> for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR;
> _pte++, addr += PAGE_SIZE) {
> pte_t pteval = ptep_get(_pte);
> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
> - ++none_or_zero;
> - if (!userfaultfd_armed(vma) &&
> - (!cc->is_khugepaged ||
> - none_or_zero <= khugepaged_max_ptes_none)) {
> - continue;
> - } else {
> - result = SCAN_EXCEED_NONE_PTE;
> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
> - goto out_unmap;
> - }
> - } else if (!pte_present(pteval)) {
> - if (non_swap_entry(pte_to_swp_entry(pteval))) {
> - result = SCAN_PTE_NON_PRESENT;
> - goto out_unmap;
> - }
>
> - ++unmapped;
> - if (!cc->is_khugepaged ||
> - unmapped <= khugepaged_max_ptes_swap) {
> - /*
> - * Always be strict with uffd-wp
> - * enabled swap entries. Please see
> - * comment below for pte_uffd_wp().
> - */
> - if (pte_swp_uffd_wp(pteval)) {
> - result = SCAN_PTE_UFFD_WP;
> - goto out_unmap;
> - }
> - continue;
> - } else {
> - result = SCAN_EXCEED_SWAP_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
> - goto out_unmap;
> - }
> - } else if (pte_uffd_wp(pteval)) {
> - /*
> - * Don't collapse the page if any of the small
> - * PTEs are armed with uffd write protection.
> - * Here we can also mark the new huge pmd as
> - * write protected if any of the small ones is
> - * marked but that could bring unknown
> - * userfault messages that falls outside of
> - * the registered range. So, just be simple.
> - */
> - result = SCAN_PTE_UFFD_WP;
> - goto out_unmap;
> - }
> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
> + &folio, &none_or_zero, &unmapped,
> + &shared, &result, cc);
>
> - page = vm_normal_page(vma, addr, pteval);
> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> - result = SCAN_PAGE_NULL;
> - goto out_unmap;
> - }
> - folio = page_folio(page);
> -
> - if (!folio_test_anon(folio)) {
> - VM_WARN_ON_FOLIO(true, folio);
> - result = SCAN_PAGE_ANON;
> + if (pte_check_res == PTE_CHECK_CONTINUE)
> + continue;
> + else if (pte_check_res == PTE_CHECK_FAIL)
> goto out_unmap;
> - }
> -
> - /*
> - * We treat a single page as shared if any part of the THP
> - * is shared.
> - */
> - if (folio_maybe_mapped_shared(folio)) {
> - ++shared;
> - if (cc->is_khugepaged &&
> - shared > khugepaged_max_ptes_shared) {
> - result = SCAN_EXCEED_SHARED_PTE;
> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
> - goto out_unmap;
> - }
> - }
>
> /*
> * Record which node the original page is from and save this
> --
> 2.49.0
>
^ permalink raw reply [flat|nested] 19+ messages in thread* Re: [PATCH mm-new v3 3/3] mm/khugepaged: merge PTE scanning logic into a new helper
2025-10-14 17:41 ` Lorenzo Stoakes
@ 2025-10-15 1:48 ` Lance Yang
0 siblings, 0 replies; 19+ messages in thread
From: Lance Yang @ 2025-10-15 1:48 UTC (permalink / raw)
To: Lorenzo Stoakes
Cc: akpm, david, ziy, baolin.wang, Liam.Howlett, npache,
ryan.roberts, dev.jain, baohua, ioworker0, richard.weiyang,
linux-kernel, linux-mm
On 2025/10/15 01:41, Lorenzo Stoakes wrote:
> OK so this patch _is_ based on [0] already being applied then?
>
> I don't see any is_swap_pte() here so presumably so right?
>
> Can we just respin these series and put them together? Because now I've
> reviewed a bunch of stuff in [0], which this series depends upon, and
> you're saying we should now review on this instead of that and it's a bit
> of a mess.
>
> Once review here is dealt with can you combine [0] into this series please?
Got it, thanks!
>
> For [0] I would like you to reinstate the is_swap_pte() conditional as
> (copiously :) discussed over there.
>
> [0}: https://lore.kernel.org/all/20251008032657.72406-1-lance.yang@linux.dev/
>
> Thanks, Lorenzo
>
> On Wed, Oct 08, 2025 at 12:37:48PM +0800, Lance Yang wrote:
>> From: Lance Yang <lance.yang@linux.dev>
>>
>> As David suggested, the PTE scanning logic in hpage_collapse_scan_pmd()
>> and __collapse_huge_page_isolate() was almost duplicated.
>>
>> This patch cleans things up by moving all the common PTE checking logic
>> into a new shared helper, thp_collapse_check_pte(). While at it, we use
>> vm_normal_folio() instead of vm_normal_page().
>>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Suggested-by: Dev Jain <dev.jain@arm.com>
>> Signed-off-by: Lance Yang <lance.yang@linux.dev>
>> ---
>> mm/khugepaged.c | 243 ++++++++++++++++++++++++++----------------------
>> 1 file changed, 130 insertions(+), 113 deletions(-)
>>
>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>> index b5c0295c3414..7116caae1fa4 100644
>> --- a/mm/khugepaged.c
>> +++ b/mm/khugepaged.c
>> @@ -61,6 +61,12 @@ enum scan_result {
>> SCAN_PAGE_FILLED,
>> };
>>
>> +enum pte_check_result {
>> + PTE_CHECK_SUCCEED,
>> + PTE_CHECK_CONTINUE,
>> + PTE_CHECK_FAIL,
>> +};
>> +
>> #define CREATE_TRACE_POINTS
>> #include <trace/events/huge_memory.h>
>>
>> @@ -533,62 +539,139 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte,
>> }
>> }
>>
>> +/*
>> + * thp_collapse_check_pte - Check if a PTE is suitable for THP collapse
>> + * @pte: The PTE to check
>> + * @vma: The VMA the PTE belongs to
>> + * @addr: The virtual address corresponding to this PTE
>> + * @foliop: On success, used to return a pointer to the folio
>> + * Must be non-NULL
>> + * @none_or_zero: Counter for none/zero PTEs. Must be non-NULL
>> + * @unmapped: Counter for swap PTEs. Can be NULL if not scanning swaps
>> + * @shared: Counter for shared pages. Must be non-NULL
>> + * @scan_result: Used to return the failure reason (SCAN_*) on a
>> + * PTE_CHECK_FAIL return. Must be non-NULL
>> + * @cc: Collapse control settings
>> + *
>> + * Returns:
>> + * PTE_CHECK_SUCCEED - PTE is suitable, proceed with further checks
>> + * PTE_CHECK_CONTINUE - Skip this PTE and continue scanning
>> + * PTE_CHECK_FAIL - Abort collapse scan
>> + */
>> +static inline int thp_collapse_check_pte(pte_t pte, struct vm_area_struct *vma,
>> + unsigned long addr, struct folio **foliop, int *none_or_zero,
>> + int *unmapped, int *shared, int *scan_result,
>> + struct collapse_control *cc)
>> +{
>> + struct folio *folio = NULL;
>> +
>> + if (pte_none(pte) || is_zero_pfn(pte_pfn(pte))) {
>> + (*none_or_zero)++;
>> + if (!userfaultfd_armed(vma) &&
>> + (!cc->is_khugepaged ||
>> + *none_or_zero <= khugepaged_max_ptes_none)) {
>> + return PTE_CHECK_CONTINUE;
>> + } else {
>> + *scan_result = SCAN_EXCEED_NONE_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + } else if (!pte_present(pte)) {
>> + if (!unmapped) {
>> + *scan_result = SCAN_PTE_NON_PRESENT;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + if (non_swap_entry(pte_to_swp_entry(pte))) {
>> + *scan_result = SCAN_PTE_NON_PRESENT;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + (*unmapped)++;
>> + if (!cc->is_khugepaged ||
>> + *unmapped <= khugepaged_max_ptes_swap) {
>> + /*
>> + * Always be strict with uffd-wp enabled swap
>> + * entries. Please see comment below for
>> + * pte_uffd_wp().
>> + */
>> + if (pte_swp_uffd_wp(pte)) {
>> + *scan_result = SCAN_PTE_UFFD_WP;
>> + return PTE_CHECK_FAIL;
>> + }
>> + return PTE_CHECK_CONTINUE;
>> + } else {
>> + *scan_result = SCAN_EXCEED_SWAP_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + } else if (pte_uffd_wp(pte)) {
>> + /*
>> + * Don't collapse the page if any of the small PTEs are
>> + * armed with uffd write protection. Here we can also mark
>> + * the new huge pmd as write protected if any of the small
>> + * ones is marked but that could bring unknown userfault
>> + * messages that falls outside of the registered range.
>> + * So, just be simple.
>> + */
>> + *scan_result = SCAN_PTE_UFFD_WP;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + folio = vm_normal_folio(vma, addr, pte);
>> + if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
>> + *scan_result = SCAN_PAGE_NULL;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + if (!folio_test_anon(folio)) {
>> + VM_WARN_ON_FOLIO(true, folio);
>> + *scan_result = SCAN_PAGE_ANON;
>> + return PTE_CHECK_FAIL;
>> + }
>> +
>> + /*
>> + * We treat a single page as shared if any part of the THP
>> + * is shared.
>> + */
>> + if (folio_maybe_mapped_shared(folio)) {
>> + (*shared)++;
>> + if (cc->is_khugepaged && *shared > khugepaged_max_ptes_shared) {
>> + *scan_result = SCAN_EXCEED_SHARED_PTE;
>> + count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
>> + return PTE_CHECK_FAIL;
>> + }
>> + }
>> +
>> + *foliop = folio;
>> +
>> + return PTE_CHECK_SUCCEED;
>> +}
>> +
>> static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>> unsigned long start_addr,
>> pte_t *pte,
>> struct collapse_control *cc,
>> struct list_head *compound_pagelist)
>> {
>> - struct page *page = NULL;
>> struct folio *folio = NULL;
>> unsigned long addr = start_addr;
>> pte_t *_pte;
>> int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
>> + int pte_check_res;
>>
>> for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
>> _pte++, addr += PAGE_SIZE) {
>> pte_t pteval = ptep_get(_pte);
>> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
>> - ++none_or_zero;
>> - if (!userfaultfd_armed(vma) &&
>> - (!cc->is_khugepaged ||
>> - none_or_zero <= khugepaged_max_ptes_none)) {
>> - continue;
>> - } else {
>> - result = SCAN_EXCEED_NONE_PTE;
>> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>> - goto out;
>> - }
>> - } else if (!pte_present(pteval)) {
>> - result = SCAN_PTE_NON_PRESENT;
>> - goto out;
>> - } else if (pte_uffd_wp(pteval)) {
>> - result = SCAN_PTE_UFFD_WP;
>> - goto out;
>> - }
>> - page = vm_normal_page(vma, addr, pteval);
>> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
>> - result = SCAN_PAGE_NULL;
>> - goto out;
>> - }
>>
>> - folio = page_folio(page);
>> - if (!folio_test_anon(folio)) {
>> - VM_WARN_ON_FOLIO(true, folio);
>> - result = SCAN_PAGE_ANON;
>> - goto out;
>> - }
>> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
>> + &folio, &none_or_zero, NULL, &shared,
>> + &result, cc);
>>
>> - /* See hpage_collapse_scan_pmd(). */
>> - if (folio_maybe_mapped_shared(folio)) {
>> - ++shared;
>> - if (cc->is_khugepaged &&
>> - shared > khugepaged_max_ptes_shared) {
>> - result = SCAN_EXCEED_SHARED_PTE;
>> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
>> - goto out;
>> - }
>> - }
>> + if (pte_check_res == PTE_CHECK_CONTINUE)
>> + continue;
>> + else if (pte_check_res == PTE_CHECK_FAIL)
>> + goto out;
>>
>> if (folio_test_large(folio)) {
>> struct folio *f;
>> @@ -1264,11 +1347,11 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>> pte_t *pte, *_pte;
>> int result = SCAN_FAIL, referenced = 0;
>> int none_or_zero = 0, shared = 0;
>> - struct page *page = NULL;
>> struct folio *folio = NULL;
>> unsigned long addr;
>> spinlock_t *ptl;
>> int node = NUMA_NO_NODE, unmapped = 0;
>> + int pte_check_res;
>>
>> VM_BUG_ON(start_addr & ~HPAGE_PMD_MASK);
>>
>> @@ -1287,81 +1370,15 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>> for (addr = start_addr, _pte = pte; _pte < pte + HPAGE_PMD_NR;
>> _pte++, addr += PAGE_SIZE) {
>> pte_t pteval = ptep_get(_pte);
>> - if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) {
>> - ++none_or_zero;
>> - if (!userfaultfd_armed(vma) &&
>> - (!cc->is_khugepaged ||
>> - none_or_zero <= khugepaged_max_ptes_none)) {
>> - continue;
>> - } else {
>> - result = SCAN_EXCEED_NONE_PTE;
>> - count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
>> - goto out_unmap;
>> - }
>> - } else if (!pte_present(pteval)) {
>> - if (non_swap_entry(pte_to_swp_entry(pteval))) {
>> - result = SCAN_PTE_NON_PRESENT;
>> - goto out_unmap;
>> - }
>>
>> - ++unmapped;
>> - if (!cc->is_khugepaged ||
>> - unmapped <= khugepaged_max_ptes_swap) {
>> - /*
>> - * Always be strict with uffd-wp
>> - * enabled swap entries. Please see
>> - * comment below for pte_uffd_wp().
>> - */
>> - if (pte_swp_uffd_wp(pteval)) {
>> - result = SCAN_PTE_UFFD_WP;
>> - goto out_unmap;
>> - }
>> - continue;
>> - } else {
>> - result = SCAN_EXCEED_SWAP_PTE;
>> - count_vm_event(THP_SCAN_EXCEED_SWAP_PTE);
>> - goto out_unmap;
>> - }
>> - } else if (pte_uffd_wp(pteval)) {
>> - /*
>> - * Don't collapse the page if any of the small
>> - * PTEs are armed with uffd write protection.
>> - * Here we can also mark the new huge pmd as
>> - * write protected if any of the small ones is
>> - * marked but that could bring unknown
>> - * userfault messages that falls outside of
>> - * the registered range. So, just be simple.
>> - */
>> - result = SCAN_PTE_UFFD_WP;
>> - goto out_unmap;
>> - }
>> + pte_check_res = thp_collapse_check_pte(pteval, vma, addr,
>> + &folio, &none_or_zero, &unmapped,
>> + &shared, &result, cc);
>>
>> - page = vm_normal_page(vma, addr, pteval);
>> - if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
>> - result = SCAN_PAGE_NULL;
>> - goto out_unmap;
>> - }
>> - folio = page_folio(page);
>> -
>> - if (!folio_test_anon(folio)) {
>> - VM_WARN_ON_FOLIO(true, folio);
>> - result = SCAN_PAGE_ANON;
>> + if (pte_check_res == PTE_CHECK_CONTINUE)
>> + continue;
>> + else if (pte_check_res == PTE_CHECK_FAIL)
>> goto out_unmap;
>> - }
>> -
>> - /*
>> - * We treat a single page as shared if any part of the THP
>> - * is shared.
>> - */
>> - if (folio_maybe_mapped_shared(folio)) {
>> - ++shared;
>> - if (cc->is_khugepaged &&
>> - shared > khugepaged_max_ptes_shared) {
>> - result = SCAN_EXCEED_SHARED_PTE;
>> - count_vm_event(THP_SCAN_EXCEED_SHARED_PTE);
>> - goto out_unmap;
>> - }
>> - }
>>
>> /*
>> * Record which node the original page is from and save this
>> --
>> 2.49.0
>>
^ permalink raw reply [flat|nested] 19+ messages in thread