[PATCH 03/10] mm/madvise: factor shared LRU folio handling

[Gregory Price]

The huge-PMD and PTE paths duplicate folio filtering, reference clearing,
deactivation and pageout isolation. Keeping both copies synchronized
obscures the page-table-specific control flow.

Factor the common filtering and LRU operation into helpers. Keep the
lock-before-reference sequence visible at each split site because an early
reference can prevent split_folio() from succeeding.

No functional change intended.

Assisted-by: LLM
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
---
 mm/madvise.c | 90 +++++++++++++++++++++++++---------------------------
 1 file changed, 43 insertions(+), 47 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 83d54ab385da8..c345fef23f15d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -361,6 +361,39 @@ static inline int madvise_folio_pte_batch(unsigned long addr, unsigned long end,
 				     FPB_MERGE_YOUNG_DIRTY);
 }
 
+static inline void
+madvise_lru_folio(struct folio *folio, bool pageout,
+		struct list_head *folio_list)
+{
+	/*
+	 * Clear references before deactivating or reclaiming the folio. This can
+	 * make idle-page tracking miss recent accesses.
+	 */
+	folio_clear_referenced(folio);
+	folio_test_clear_young(folio);
+	if (folio_test_active(folio))
+		folio_set_workingset(folio);
+
+	if (!pageout) {
+		folio_deactivate(folio);
+		return;
+	}
+
+	if (!folio_isolate_lru(folio))
+		return;
+	if (folio_test_unevictable(folio))
+		folio_putback_lru(folio);
+	else
+		list_add(&folio->lru, folio_list);
+}
+
+static bool madvise_lru_folio_is_filtered(struct folio *folio,
+		bool pageout_anon_only)
+{
+	return folio_maybe_mapped_shared(folio) ||
+	       (pageout_anon_only && !folio_test_anon(folio));
+}
+
 static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 		unsigned long end, struct mm_walk *walk)
 {
@@ -373,15 +406,14 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 	spinlock_t *ptl;
 	struct folio *folio = NULL;
 	LIST_HEAD(folio_list);
-	bool pageout_anon_only_filter;
 	unsigned int batch_count = 0;
+	bool pageout_anon_only;
 	int nr;
 
 	if (fatal_signal_pending(current))
 		return -EINTR;
-
-	pageout_anon_only_filter = pageout && !vma_is_anonymous(vma) &&
-					!can_do_file_pageout(vma);
+	pageout_anon_only = pageout && !vma_is_anonymous(vma) &&
+				       !can_do_file_pageout(vma);
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	if (pmd_trans_huge(*pmd)) {
@@ -407,11 +439,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 		if (folio_is_zone_device(folio))
 			goto huge_unlock;
 
-		/* Do not interfere with other mappings of this folio */
-		if (folio_maybe_mapped_shared(folio))
-			goto huge_unlock;
-
-		if (pageout_anon_only_filter && !folio_test_anon(folio))
+		if (madvise_lru_folio_is_filtered(folio, pageout_anon_only))
 			goto huge_unlock;
 
 		if (next - addr != HPAGE_PMD_SIZE) {
@@ -437,19 +465,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 			tlb_remove_pmd_tlb_entry(tlb, pmd, addr);
 		}
 
-		folio_clear_referenced(folio);
-		folio_test_clear_young(folio);
-		if (folio_test_active(folio))
-			folio_set_workingset(folio);
-		if (pageout) {
-			if (folio_isolate_lru(folio)) {
-				if (folio_test_unevictable(folio))
-					folio_putback_lru(folio);
-				else
-					list_add(&folio->lru, &folio_list);
-			}
-		} else
-			folio_deactivate(folio);
+		madvise_lru_folio(folio, pageout, &folio_list);
 huge_unlock:
 		spin_unlock(ptl);
 		if (pageout)
@@ -502,9 +518,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 			if (nr < folio_nr_pages(folio)) {
 				int err;
 
-				if (folio_maybe_mapped_shared(folio))
-					continue;
-				if (pageout_anon_only_filter && !folio_test_anon(folio))
+				if (madvise_lru_folio_is_filtered(folio, pageout_anon_only))
 					continue;
 				if (!folio_trylock(folio))
 					continue;
@@ -537,7 +551,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 		    folio_mapcount(folio) != folio_nr_pages(folio))
 			continue;
 
-		if (pageout_anon_only_filter && !folio_test_anon(folio))
+		if (pageout_anon_only && !folio_test_anon(folio))
 			continue;
 
 		if (!pageout && pte_young(ptent)) {
@@ -546,25 +560,7 @@ static int madvise_lru_pmd_entry(pmd_t *pmd, unsigned long addr,
 			tlb_remove_tlb_entries(tlb, pte, nr, addr);
 		}
 
-		/*
-		 * We are deactivating a folio for accelerating reclaiming.
-		 * VM couldn't reclaim the folio unless we clear PG_young.
-		 * As a side effect, it makes confuse idle-page tracking
-		 * because they will miss recent referenced history.
-		 */
-		folio_clear_referenced(folio);
-		folio_test_clear_young(folio);
-		if (folio_test_active(folio))
-			folio_set_workingset(folio);
-		if (pageout) {
-			if (folio_isolate_lru(folio)) {
-				if (folio_test_unevictable(folio))
-					folio_putback_lru(folio);
-				else
-					list_add(&folio->lru, &folio_list);
-			}
-		} else
-			folio_deactivate(folio);
+		madvise_lru_folio(folio, pageout, &folio_list);
 	}
 
 out:
@@ -651,8 +647,8 @@ static long madvise_pageout(struct madvise_behavior *madv_behavior)
 	 * owner nor write capable of the file. We allow private file mappings
 	 * further to pageout dirty anon pages.
 	 */
-	if (!vma_is_anonymous(vma) && (!can_do_file_pageout(vma) &&
-				(vma->vm_flags & VM_MAYSHARE)))
+	if (!vma_is_anonymous(vma) && !can_do_file_pageout(vma) &&
+	    (vma->vm_flags & VM_MAYSHARE))
 		return 0;
 
 	lru_add_drain();
-- 
2.53.0-Meta