[PATCH 2/3] mm/lru_gen: lru_gen_look_around simplification

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

To store generation details in folio_flags we need lru_gen_mm_walk
structure in which we batch the nr_pages update. A follow-up patch wants to
avoid compiling all the lru_gen mm walk-related code on architectures that
don't support it. Split out the look-around generation update by marking
folio active into a separate helper which will be used in that case.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 mm/vmscan.c | 57 +++++++++++++++++++++++++++++++++++------------------
 1 file changed, 38 insertions(+), 19 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index edfe073b475e..f277beba556c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4619,6 +4619,39 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
  *                          rmap/PT walk feedback
  ******************************************************************************/
 
+static void __look_around_gen_update(struct folio *folio, int new_gen)
+{
+	int old_gen;
+
+	old_gen = folio_lru_gen(folio);
+	if (old_gen < 0)
+		folio_set_referenced(folio);
+	else if (old_gen != new_gen)
+		folio_activate(folio);
+}
+
+static inline bool current_reclaim_state_can_swap(void)
+{
+	if (current->reclaim_state)
+		return current->reclaim_state->mm_walk->can_swap;
+	return true;
+}
+
+static void look_around_gen_update(struct folio *folio, int new_gen)
+{
+	int old_gen;
+	struct lru_gen_mm_walk *walk;
+
+	walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL;
+	if (walk) {
+		old_gen = folio_update_gen(folio, new_gen);
+		if (old_gen >= 0 && old_gen != new_gen)
+			update_batch_size(walk, folio, old_gen, new_gen);
+		return;
+	}
+	return __look_around_gen_update(folio, new_gen);
+}
+
 /*
  * This function exploits spatial locality when shrink_folio_list() walks the
  * rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages. If
@@ -4631,7 +4664,6 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	int i;
 	unsigned long start;
 	unsigned long end;
-	struct lru_gen_mm_walk *walk;
 	int young = 0;
 	pte_t *pte = pvmw->pte;
 	unsigned long addr = pvmw->address;
@@ -4640,7 +4672,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	struct pglist_data *pgdat = folio_pgdat(folio);
 	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
 	DEFINE_MAX_SEQ(lruvec);
-	int old_gen, new_gen = lru_gen_from_seq(max_seq);
+	int new_gen = lru_gen_from_seq(max_seq);
 
 	lockdep_assert_held(pvmw->ptl);
 	VM_WARN_ON_ONCE_FOLIO(folio_test_lru(folio), folio);
@@ -4648,9 +4680,6 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	if (spin_is_contended(pvmw->ptl))
 		return;
 
-	/* avoid taking the LRU lock under the PTL when possible */
-	walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL;
-
 	start = max(addr & PMD_MASK, pvmw->vma->vm_start);
 	end = min(addr | ~PMD_MASK, pvmw->vma->vm_end - 1) + 1;
 
@@ -4683,7 +4712,9 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 		if (!pte_young(pte[i]))
 			continue;
 
-		folio = get_pfn_folio(pfn, memcg, pgdat, !walk || walk->can_swap);
+		folio = get_pfn_folio(pfn, memcg, pgdat,
+				      current_reclaim_state_can_swap());
+
 		if (!folio)
 			continue;
 
@@ -4697,19 +4728,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 		      !folio_test_swapcache(folio)))
 			folio_mark_dirty(folio);
 
-		if (walk) {
-			old_gen = folio_update_gen(folio, new_gen);
-			if (old_gen >= 0 && old_gen != new_gen)
-				update_batch_size(walk, folio, old_gen, new_gen);
-
-			continue;
-		}
-
-		old_gen = folio_lru_gen(folio);
-		if (old_gen < 0)
-			folio_set_referenced(folio);
-		else if (old_gen != new_gen)
-			folio_activate(folio);
+		look_around_gen_update(folio, new_gen);
 	}
 
 	arch_leave_lazy_mmu_mode();
-- 
2.40.1