Re: [PATCH v2 2/2] mm: Drop all references of writable and SCAN_PAGE_RO

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 08/09/25 1:20 PM, Dev Jain wrote:
> Now that all actionable outcomes from checking pte_write() are gone,
> drop the related references.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> Acked-by: Zi Yan <ziy@nvidia.com>
> Reviewed-by: Kiryl Shutsemau <kas@kernel.org>
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Signed-off-by: Dev Jain <dev.jain@arm.com>

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

> ---
>  include/trace/events/huge_memory.h | 19 ++++++-------------
>  mm/khugepaged.c                    | 14 +++-----------
>  2 files changed, 9 insertions(+), 24 deletions(-)
> 
> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> index 2305df6cb485..dd94d14a2427 100644
> --- a/include/trace/events/huge_memory.h
> +++ b/include/trace/events/huge_memory.h
> @@ -19,7 +19,6 @@
>  	EM( SCAN_PTE_NON_PRESENT,	"pte_non_present")		\
>  	EM( SCAN_PTE_UFFD_WP,		"pte_uffd_wp")			\
>  	EM( SCAN_PTE_MAPPED_HUGEPAGE,	"pte_mapped_hugepage")		\
> -	EM( SCAN_PAGE_RO,		"no_writable_page")		\
>  	EM( SCAN_LACK_REFERENCED_PAGE,	"lack_referenced_page")		\
>  	EM( SCAN_PAGE_NULL,		"page_null")			\
>  	EM( SCAN_SCAN_ABORT,		"scan_aborted")			\
> @@ -55,15 +54,14 @@ SCAN_STATUS
>  
>  TRACE_EVENT(mm_khugepaged_scan_pmd,
>  
> -	TP_PROTO(struct mm_struct *mm, struct folio *folio, bool writable,
> +	TP_PROTO(struct mm_struct *mm, struct folio *folio,
>  		 int referenced, int none_or_zero, int status, int unmapped),
>  
> -	TP_ARGS(mm, folio, writable, referenced, none_or_zero, status, unmapped),
> +	TP_ARGS(mm, folio, referenced, none_or_zero, status, unmapped),
>  
>  	TP_STRUCT__entry(
>  		__field(struct mm_struct *, mm)
>  		__field(unsigned long, pfn)
> -		__field(bool, writable)
>  		__field(int, referenced)
>  		__field(int, none_or_zero)
>  		__field(int, status)
> @@ -73,17 +71,15 @@ TRACE_EVENT(mm_khugepaged_scan_pmd,
>  	TP_fast_assign(
>  		__entry->mm = mm;
>  		__entry->pfn = folio ? folio_pfn(folio) : -1;
> -		__entry->writable = writable;
>  		__entry->referenced = referenced;
>  		__entry->none_or_zero = none_or_zero;
>  		__entry->status = status;
>  		__entry->unmapped = unmapped;
>  	),
>  
> -	TP_printk("mm=%p, scan_pfn=0x%lx, writable=%d, referenced=%d, none_or_zero=%d, status=%s, unmapped=%d",
> +	TP_printk("mm=%p, scan_pfn=0x%lx, referenced=%d, none_or_zero=%d, status=%s, unmapped=%d",
>  		__entry->mm,
>  		__entry->pfn,
> -		__entry->writable,
>  		__entry->referenced,
>  		__entry->none_or_zero,
>  		__print_symbolic(__entry->status, SCAN_STATUS),
> @@ -117,15 +113,14 @@ TRACE_EVENT(mm_collapse_huge_page,
>  TRACE_EVENT(mm_collapse_huge_page_isolate,
>  
>  	TP_PROTO(struct folio *folio, int none_or_zero,
> -		 int referenced, bool  writable, int status),
> +		 int referenced, int status),
>  
> -	TP_ARGS(folio, none_or_zero, referenced, writable, status),
> +	TP_ARGS(folio, none_or_zero, referenced, status),
>  
>  	TP_STRUCT__entry(
>  		__field(unsigned long, pfn)
>  		__field(int, none_or_zero)
>  		__field(int, referenced)
> -		__field(bool, writable)
>  		__field(int, status)
>  	),
>  
> @@ -133,15 +128,13 @@ TRACE_EVENT(mm_collapse_huge_page_isolate,
>  		__entry->pfn = folio ? folio_pfn(folio) : -1;
>  		__entry->none_or_zero = none_or_zero;
>  		__entry->referenced = referenced;
> -		__entry->writable = writable;
>  		__entry->status = status;
>  	),
>  
> -	TP_printk("scan_pfn=0x%lx, none_or_zero=%d, referenced=%d, writable=%d, status=%s",
> +	TP_printk("scan_pfn=0x%lx, none_or_zero=%d, referenced=%d, status=%s",
>  		__entry->pfn,
>  		__entry->none_or_zero,
>  		__entry->referenced,
> -		__entry->writable,
>  		__print_symbolic(__entry->status, SCAN_STATUS))
>  );
>  
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index a0f1df2a7ae6..af5f5c80fe4e 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -39,7 +39,6 @@ enum scan_result {
>  	SCAN_PTE_NON_PRESENT,
>  	SCAN_PTE_UFFD_WP,
>  	SCAN_PTE_MAPPED_HUGEPAGE,
> -	SCAN_PAGE_RO,
>  	SCAN_LACK_REFERENCED_PAGE,
>  	SCAN_PAGE_NULL,
>  	SCAN_SCAN_ABORT,
> @@ -557,7 +556,6 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  	struct folio *folio = NULL;
>  	pte_t *_pte;
>  	int none_or_zero = 0, shared = 0, result = SCAN_FAIL, referenced = 0;
> -	bool writable = false;
>  
>  	for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
>  	     _pte++, address += PAGE_SIZE) {
> @@ -671,9 +669,6 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  		     folio_test_referenced(folio) || mmu_notifier_test_young(vma->vm_mm,
>  								     address)))
>  			referenced++;
> -
> -		if (pte_write(pteval))
> -			writable = true;
>  	}
>  
>  	if (unlikely(cc->is_khugepaged && !referenced)) {
> @@ -681,13 +676,13 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  	} else {
>  		result = SCAN_SUCCEED;
>  		trace_mm_collapse_huge_page_isolate(folio, none_or_zero,
> -						    referenced, writable, result);
> +						    referenced, result);
>  		return result;
>  	}
>  out:
>  	release_pte_pages(pte, _pte, compound_pagelist);
>  	trace_mm_collapse_huge_page_isolate(folio, none_or_zero,
> -					    referenced, writable, result);
> +					    referenced, result);
>  	return result;
>  }
>  
> @@ -1280,7 +1275,6 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>  	unsigned long _address;
>  	spinlock_t *ptl;
>  	int node = NUMA_NO_NODE, unmapped = 0;
> -	bool writable = false;
>  
>  	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
>  
> @@ -1344,8 +1338,6 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>  			result = SCAN_PTE_UFFD_WP;
>  			goto out_unmap;
>  		}
> -		if (pte_write(pteval))
> -			writable = true;
>  
>  		page = vm_normal_page(vma, _address, pteval);
>  		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
> @@ -1435,7 +1427,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>  		*mmap_locked = false;
>  	}
>  out:
> -	trace_mm_khugepaged_scan_pmd(mm, folio, writable, referenced,
> +	trace_mm_khugepaged_scan_pmd(mm, folio, referenced,
>  				     none_or_zero, result, unmapped);
>  	return result;
>  }