mm: drop all references of writable and SCAN_PAGE_RO

Now that all actionable outcomes from checking pte_write() are gone, drop
the related references.

Link: https://lkml.kernel.org/r/20250908075028.38431-3-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
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>
Reviewed-by: Zach O'Keefe <zokeefe@google.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Dev Jain

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),
@@ -117,31 +113,28 @@ 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)
 	),
 
 	TP_fast_assign(
 		__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))
 );
 

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) {
@@ -671,23 +669,20 @@ 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)) {
 		result = SCAN_LACK_REFERENCED_PAGE;
 	} 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;
 }