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Date: Wed, 20 Dec 2023 04:00:36 +0000
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Subject: [PATCH mm-unstable v1 3/4] mm/mglru: remove CONFIG_MEMCG
From: Kinsey Ho <kinseyho@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, yuzhao@google.com, 
	Kinsey Ho <kinseyho@google.com>, Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
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Remove CONFIG_MEMCG in a refactoring to improve code readability at
the cost of a few bytes in struct lru_gen_folio per node when
CONFIG_MEMCG=n.

Signed-off-by: Kinsey Ho <kinseyho@google.com>
Co-developed-by: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>
---
 include/linux/mm_types.h |  4 ---
 include/linux/mmzone.h   | 26 ++--------------
 mm/vmscan.c              | 67 +++++++++++++---------------------------
 3 files changed, 23 insertions(+), 74 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 552fa2d11c57..55b7121809ff 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1017,9 +1017,7 @@ struct lru_gen_mm_list {
 
 void lru_gen_add_mm(struct mm_struct *mm);
 void lru_gen_del_mm(struct mm_struct *mm);
-#ifdef CONFIG_MEMCG
 void lru_gen_migrate_mm(struct mm_struct *mm);
-#endif
 
 static inline void lru_gen_init_mm(struct mm_struct *mm)
 {
@@ -1050,11 +1048,9 @@ static inline void lru_gen_del_mm(struct mm_struct *mm)
 {
 }
 
-#ifdef CONFIG_MEMCG
 static inline void lru_gen_migrate_mm(struct mm_struct *mm)
 {
 }
-#endif
 
 static inline void lru_gen_init_mm(struct mm_struct *mm)
 {
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index bc3f63ec4291..28665e1b8475 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -440,14 +440,12 @@ struct lru_gen_folio {
 	atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS];
 	/* whether the multi-gen LRU is enabled */
 	bool enabled;
-#ifdef CONFIG_MEMCG
 	/* the memcg generation this lru_gen_folio belongs to */
 	u8 gen;
 	/* the list segment this lru_gen_folio belongs to */
 	u8 seg;
 	/* per-node lru_gen_folio list for global reclaim */
 	struct hlist_nulls_node list;
-#endif
 };
 
 enum {
@@ -493,11 +491,6 @@ struct lru_gen_mm_walk {
 	bool force_scan;
 };
 
-void lru_gen_init_lruvec(struct lruvec *lruvec);
-void lru_gen_look_around(struct page_vma_mapped_walk *pvmw);
-
-#ifdef CONFIG_MEMCG
-
 /*
  * For each node, memcgs are divided into two generations: the old and the
  * young. For each generation, memcgs are randomly sharded into multiple bins
@@ -555,6 +548,8 @@ struct lru_gen_memcg {
 };
 
 void lru_gen_init_pgdat(struct pglist_data *pgdat);
+void lru_gen_init_lruvec(struct lruvec *lruvec);
+void lru_gen_look_around(struct page_vma_mapped_walk *pvmw);
 
 void lru_gen_init_memcg(struct mem_cgroup *memcg);
 void lru_gen_exit_memcg(struct mem_cgroup *memcg);
@@ -563,19 +558,6 @@ void lru_gen_offline_memcg(struct mem_cgroup *memcg);
 void lru_gen_release_memcg(struct mem_cgroup *memcg);
 void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid);
 
-#else /* !CONFIG_MEMCG */
-
-#define MEMCG_NR_GENS	1
-
-struct lru_gen_memcg {
-};
-
-static inline void lru_gen_init_pgdat(struct pglist_data *pgdat)
-{
-}
-
-#endif /* CONFIG_MEMCG */
-
 #else /* !CONFIG_LRU_GEN */
 
 static inline void lru_gen_init_pgdat(struct pglist_data *pgdat)
@@ -590,8 +572,6 @@ static inline void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 {
 }
 
-#ifdef CONFIG_MEMCG
-
 static inline void lru_gen_init_memcg(struct mem_cgroup *memcg)
 {
 }
@@ -616,8 +596,6 @@ static inline void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid)
 {
 }
 
-#endif /* CONFIG_MEMCG */
-
 #endif /* CONFIG_LRU_GEN */
 
 struct lruvec {
diff --git a/mm/vmscan.c b/mm/vmscan.c
index aa7ea09ffb4c..351a0b5043c0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4097,13 +4097,6 @@ enum {
 	MEMCG_LRU_YOUNG,
 };
 
-#ifdef CONFIG_MEMCG
-
-static int lru_gen_memcg_seg(struct lruvec *lruvec)
-{
-	return READ_ONCE(lruvec->lrugen.seg);
-}
-
 static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 {
 	int seg;
@@ -4150,6 +4143,8 @@ static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
 	spin_unlock_irqrestore(&pgdat->memcg_lru.lock, flags);
 }
 
+#ifdef CONFIG_MEMCG
+
 void lru_gen_online_memcg(struct mem_cgroup *memcg)
 {
 	int gen;
@@ -4217,18 +4212,11 @@ void lru_gen_soft_reclaim(struct mem_cgroup *memcg, int nid)
 	struct lruvec *lruvec = get_lruvec(memcg, nid);
 
 	/* see the comment on MEMCG_NR_GENS */
-	if (lru_gen_memcg_seg(lruvec) != MEMCG_LRU_HEAD)
+	if (READ_ONCE(lruvec->lrugen.seg) != MEMCG_LRU_HEAD)
 		lru_gen_rotate_memcg(lruvec, MEMCG_LRU_HEAD);
 }
 
-#else /* !CONFIG_MEMCG */
-
-static int lru_gen_memcg_seg(struct lruvec *lruvec)
-{
-	return 0;
-}
-
-#endif
+#endif /* CONFIG_MEMCG */
 
 /******************************************************************************
  *                          the eviction
@@ -4776,7 +4764,7 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
 
 	if (mem_cgroup_below_low(NULL, memcg)) {
 		/* see the comment on MEMCG_NR_GENS */
-		if (lru_gen_memcg_seg(lruvec) != MEMCG_LRU_TAIL)
+		if (READ_ONCE(lruvec->lrugen.seg) != MEMCG_LRU_TAIL)
 			return MEMCG_LRU_TAIL;
 
 		memcg_memory_event(memcg, MEMCG_LOW);
@@ -4799,12 +4787,10 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc)
 		return 0;
 
 	/* one retry if offlined or too small */
-	return lru_gen_memcg_seg(lruvec) != MEMCG_LRU_TAIL ?
+	return READ_ONCE(lruvec->lrugen.seg) != MEMCG_LRU_TAIL ?
 	       MEMCG_LRU_TAIL : MEMCG_LRU_YOUNG;
 }
 
-#ifdef CONFIG_MEMCG
-
 static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
 {
 	int op;
@@ -4896,20 +4882,6 @@ static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc
 	blk_finish_plug(&plug);
 }
 
-#else /* !CONFIG_MEMCG */
-
-static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc)
-{
-	BUILD_BUG();
-}
-
-static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
-{
-	BUILD_BUG();
-}
-
-#endif
-
 static void set_initial_priority(struct pglist_data *pgdat, struct scan_control *sc)
 {
 	int priority;
@@ -5560,6 +5532,18 @@ static const struct file_operations lru_gen_ro_fops = {
  *                          initialization
  ******************************************************************************/
 
+void lru_gen_init_pgdat(struct pglist_data *pgdat)
+{
+	int i, j;
+
+	spin_lock_init(&pgdat->memcg_lru.lock);
+
+	for (i = 0; i < MEMCG_NR_GENS; i++) {
+		for (j = 0; j < MEMCG_NR_BINS; j++)
+			INIT_HLIST_NULLS_HEAD(&pgdat->memcg_lru.fifo[i][j], i);
+	}
+}
+
 void lru_gen_init_lruvec(struct lruvec *lruvec)
 {
 	int i;
@@ -5582,18 +5566,6 @@ void lru_gen_init_lruvec(struct lruvec *lruvec)
 
 #ifdef CONFIG_MEMCG
 
-void lru_gen_init_pgdat(struct pglist_data *pgdat)
-{
-	int i, j;
-
-	spin_lock_init(&pgdat->memcg_lru.lock);
-
-	for (i = 0; i < MEMCG_NR_GENS; i++) {
-		for (j = 0; j < MEMCG_NR_BINS; j++)
-			INIT_HLIST_NULLS_HEAD(&pgdat->memcg_lru.fifo[i][j], i);
-	}
-}
-
 void lru_gen_init_memcg(struct mem_cgroup *memcg)
 {
 	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
@@ -5653,14 +5625,17 @@ late_initcall(init_lru_gen);
 
 static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
 {
+	BUILD_BUG();
 }
 
 static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
+	BUILD_BUG();
 }
 
 static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control *sc)
 {
+	BUILD_BUG();
 }
 
 #endif /* CONFIG_LRU_GEN */
-- 
2.43.0.472.g3155946c3a-goog