[PATCH v4 07/13] mm/khugepaged: add flag to ignore page young/referenced requirement

["Zach O'Keefe" <zokeefe@google.com>]

Add enforce_young flag to struct collapse_control that allows context to
ignore requirement that some pages in region being collapsed be young or
referenced.  Set this flag in khugepaged collapse context to preserve
existing khugepaged behavior.

This flag will be used (unset) when introducing madvise collapse
context since here, the user presumably has reason to believe the
collapse will be beneficial and khugepaged heuristics shouldn't tell
the user they are wrong.

Signed-off-by: Zach O'Keefe <zokeefe@google.com>
---
 mm/khugepaged.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 94f18be83835..b57a4a643053 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -90,6 +90,9 @@ struct collapse_control {
 	/* Respect khugepaged_max_ptes_[none|swap|shared] */
 	bool enforce_pte_scan_limits;
 
+	/* Require memory to be young */
+	bool enforce_young;
+
 	/* Num pages scanned per node */
 	int node_load[MAX_NUMNODES];
 
@@ -720,9 +723,10 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 			list_add_tail(&page->lru, compound_pagelist);
 next:
 		/* There should be enough young pte to collapse the page */
-		if (pte_young(pteval) ||
-		    page_is_young(page) || PageReferenced(page) ||
-		    mmu_notifier_test_young(vma->vm_mm, address))
+		if (cc->enforce_young &&
+		    (pte_young(pteval) || page_is_young(page) ||
+		     PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
+								     address)))
 			referenced++;
 
 		if (pte_write(pteval))
@@ -731,7 +735,7 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
 
 	if (unlikely(!writable)) {
 		result = SCAN_PAGE_RO;
-	} else if (unlikely(!referenced)) {
+	} else if (unlikely(cc->enforce_young && !referenced)) {
 		result = SCAN_LACK_REFERENCED_PAGE;
 	} else {
 		result = SCAN_SUCCEED;
@@ -1388,14 +1392,16 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 			result = SCAN_PAGE_COUNT;
 			goto out_unmap;
 		}
-		if (pte_young(pteval) ||
-		    page_is_young(page) || PageReferenced(page) ||
-		    mmu_notifier_test_young(vma->vm_mm, address))
+		if (cc->enforce_young &&
+		    (pte_young(pteval) || page_is_young(page) ||
+		     PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
+								     address)))
 			referenced++;
 	}
 	if (!writable) {
 		result = SCAN_PAGE_RO;
-	} else if (!referenced || (unmapped && referenced < HPAGE_PMD_NR/2)) {
+	} else if (cc->enforce_young && (!referenced || (unmapped && referenced
+							 < HPAGE_PMD_NR / 2))) {
 		result = SCAN_LACK_REFERENCED_PAGE;
 	} else {
 		result = SCAN_SUCCEED;
@@ -2348,6 +2354,7 @@ static int khugepaged(void *none)
 	struct mm_slot *mm_slot;
 	struct collapse_control cc = {
 		.enforce_pte_scan_limits = true,
+		.enforce_young = true,
 		.last_target_node = NUMA_NO_NODE,
 		.alloc_charge_hpage = &alloc_charge_hpage,
 	};
-- 
2.36.0.464.gb9c8b46e94-goog