[PATCH v2 5/5] mm/mglru: Don't build multi-gen LRU page table walk code on architecture not supported

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

Not all architecture supports hardware atomic updates of access bits. On
such an arch, we don't use a page table walk to classify pages into
generations. Add a kernel config option and remove adding all the page
table walk code on such architecture.

This avoid calling lru_gen related code (lru_gen_add/remove/migrate_mm)
in fork/exit/context switch Also we don't build different components
like Bloom filter and all the page table walk code (walk_mm and related
code) on not supported architecture with this change.

No preformance change observed with mongodb ycsb test:

Patch details        Throughput(Ops/sec)
without patch		91252
With patch		91488

Without patch:
$ size mm/vmscan.o
   text    data     bss     dec     hex filename
 116016   36857      40  152913   25551 mm/vmscan.o

With patch

$ size  mm/vmscan.o
   text    data     bss     dec     hex filename
 112864   36437      40  149341   2475d mm/vmscan.o

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
---
 arch/Kconfig               |  3 +++
 arch/arm64/Kconfig         |  1 +
 arch/x86/Kconfig           |  1 +
 include/linux/memcontrol.h |  2 +-
 include/linux/mm_types.h   | 10 ++++-----
 include/linux/mmzone.h     | 12 +++++++++-
 kernel/fork.c              |  2 +-
 mm/memcontrol.c            |  2 +-
 mm/vmscan.c                | 45 ++++++++++++++++++++++++++++++++++++++
 9 files changed, 69 insertions(+), 9 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index aff2746c8af2..ec8662e2f3cb 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1471,6 +1471,9 @@ config DYNAMIC_SIGFRAME
 config HAVE_ARCH_NODE_DEV_GROUP
 	bool
 
+config LRU_TASK_PAGE_AGING
+	bool
+
 config ARCH_HAS_NONLEAF_PMD_YOUNG
 	bool
 	help
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 7856c3a3e35a..d6b5d1647baa 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -233,6 +233,7 @@ config ARM64
 	select IRQ_FORCED_THREADING
 	select KASAN_VMALLOC if KASAN
 	select LOCK_MM_AND_FIND_VMA
+	select LRU_TASK_PAGE_AGING		if LRU_GEN
 	select MODULES_USE_ELF_RELA
 	select NEED_DMA_MAP_STATE
 	select NEED_SG_DMA_LENGTH
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7422db409770..940d86a0a566 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -281,6 +281,7 @@ config X86
 	select HOTPLUG_SPLIT_STARTUP		if SMP && X86_32
 	select IRQ_FORCED_THREADING
 	select LOCK_MM_AND_FIND_VMA
+	select LRU_TASK_PAGE_AGING		if LRU_GEN
 	select NEED_PER_CPU_EMBED_FIRST_CHUNK
 	select NEED_PER_CPU_PAGE_FIRST_CHUNK
 	select NEED_SG_DMA_LENGTH
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 0ab426a5696b..5ddc1abe95ae 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -321,7 +321,7 @@ struct mem_cgroup {
 	struct deferred_split deferred_split_queue;
 #endif
 
-#ifdef CONFIG_LRU_GEN
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 	/* per-memcg mm_struct list */
 	struct lru_gen_mm_list mm_list;
 #endif
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index de10fc797c8e..9089762aa8e2 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -793,7 +793,7 @@ struct mm_struct {
 		 */
 		unsigned long ksm_rmap_items;
 #endif
-#ifdef CONFIG_LRU_GEN
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 		struct {
 			/* this mm_struct is on lru_gen_mm_list */
 			struct list_head list;
@@ -808,7 +808,7 @@ struct mm_struct {
 			struct mem_cgroup *memcg;
 #endif
 		} lru_gen;
-#endif /* CONFIG_LRU_GEN */
+#endif /* CONFIG_LRU_TASK_PAGE_AGING */
 	} __randomize_layout;
 
 	/*
@@ -837,7 +837,7 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
 	return (struct cpumask *)&mm->cpu_bitmap;
 }
 
-#ifdef CONFIG_LRU_GEN
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 
 struct lru_gen_mm_list {
 	/* mm_struct list for page table walkers */
@@ -871,7 +871,7 @@ static inline void lru_gen_use_mm(struct mm_struct *mm)
 	WRITE_ONCE(mm->lru_gen.bitmap, -1);
 }
 
-#else /* !CONFIG_LRU_GEN */
+#else /* !CONFIG_LRU_TASK_PAGE_AGING */
 
 static inline void lru_gen_add_mm(struct mm_struct *mm)
 {
@@ -895,7 +895,7 @@ static inline void lru_gen_use_mm(struct mm_struct *mm)
 {
 }
 
-#endif /* CONFIG_LRU_GEN */
+#endif /* CONFIG_LRU_TASK_PAGE_AGING */
 
 struct vma_iterator {
 	struct ma_state mas;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5e50b78d58ea..5300696d7c2c 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -461,6 +461,7 @@ enum {
 struct lru_gen_mm_state {
 	/* set to max_seq after each iteration */
 	unsigned long seq;
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 	/* where the current iteration continues after */
 	struct list_head *head;
 	/* where the last iteration ended before */
@@ -469,6 +470,11 @@ struct lru_gen_mm_state {
 	unsigned long *filters[NR_BLOOM_FILTERS];
 	/* the mm stats for debugging */
 	unsigned long stats[NR_HIST_GENS][NR_MM_STATS];
+#else
+	/* protect the seq update above */
+	/* May be we can use lruvec->lock?  */
+	spinlock_t lock;
+#endif
 };
 
 struct lru_gen_mm_walk {
@@ -546,9 +552,13 @@ struct lru_gen_memcg {
 };
 
 void lru_gen_init_pgdat(struct pglist_data *pgdat);
-
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 void lru_gen_init_memcg(struct mem_cgroup *memcg);
 void lru_gen_exit_memcg(struct mem_cgroup *memcg);
+#else
+static inline void lru_gen_init_memcg(struct mem_cgroup *memcg) {}
+static inline void lru_gen_exit_memcg(struct mem_cgroup *memcg) {}
+#endif
 void lru_gen_online_memcg(struct mem_cgroup *memcg);
 void lru_gen_offline_memcg(struct mem_cgroup *memcg);
 void lru_gen_release_memcg(struct mem_cgroup *memcg);
diff --git a/kernel/fork.c b/kernel/fork.c
index b85814e614a5..c7e8f65a72c8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2932,7 +2932,7 @@ pid_t kernel_clone(struct kernel_clone_args *args)
 		get_task_struct(p);
 	}
 
-	if (IS_ENABLED(CONFIG_LRU_GEN) && !(clone_flags & CLONE_VM)) {
+	if (IS_ENABLED(CONFIG_LRU_TASK_PAGE_AGING) && !(clone_flags & CLONE_VM)) {
 		/* lock the task to synchronize with memcg migration */
 		task_lock(p);
 		lru_gen_add_mm(p->mm);
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 92898e99e8a5..cdcf1b6baf3e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6357,7 +6357,7 @@ static void mem_cgroup_move_task(void)
 }
 #endif
 
-#ifdef CONFIG_LRU_GEN
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 static void mem_cgroup_attach(struct cgroup_taskset *tset)
 {
 	struct task_struct *task;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0ea7a07990d3..3c9f24d8a4a6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3244,10 +3244,17 @@ DEFINE_STATIC_KEY_ARRAY_FALSE(lru_gen_caps, NR_LRU_GEN_CAPS);
 #define get_cap(cap)	static_branch_unlikely(&lru_gen_caps[cap])
 #endif
 
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 static bool should_walk_mmu(void)
 {
 	return arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK);
 }
+#else
+static bool should_walk_mmu(void)
+{
+	return false;
+}
+#endif
 
 static bool should_clear_pmd_young(void)
 {
@@ -3588,6 +3595,8 @@ static void clear_mm_walk(void)
 		kfree(walk);
 }
 
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
+
 /******************************************************************************
  *                          Bloom filters
  ******************************************************************************/
@@ -4382,6 +4391,33 @@ static bool iterate_mm_list_walk(struct lruvec *lruvec, unsigned long max_seq,
 
 	return success;
 }
+#else
+
+static bool iterate_mm_list_nowalk(struct lruvec *lruvec, unsigned long max_seq)
+{
+	bool success = false;
+	struct lru_gen_mm_state *mm_state = &lruvec->mm_state;
+
+	spin_lock(&mm_state->lock);
+
+	VM_WARN_ON_ONCE(mm_state->seq + 1 < max_seq);
+
+	if (max_seq > mm_state->seq) {
+		WRITE_ONCE(mm_state->seq, mm_state->seq + 1);
+		success = true;
+	}
+
+	spin_unlock(&mm_state->lock);
+
+	return success;
+}
+
+static bool iterate_mm_list_walk(struct lruvec *lruvec, unsigned long max_seq,
+				 bool can_swap, bool force_scan)
+{
+	return false;
+}
+#endif
 
 static bool inc_min_seq(struct lruvec *lruvec, int type, bool can_swap)
 {
@@ -4744,9 +4780,11 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	arch_leave_lazy_mmu_mode();
 	mem_cgroup_unlock_pages();
 
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 	/* feedback from rmap walkers to page table walkers */
 	if (suitable_to_scan(i, young))
 		update_bloom_filter(lruvec, max_seq, pvmw->pmd);
+#endif
 }
 
 /******************************************************************************
@@ -5896,6 +5934,7 @@ static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
 		seq_putc(m, '\n');
 	}
 
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 	seq_puts(m, "                      ");
 	for (i = 0; i < NR_MM_STATS; i++) {
 		const char *s = "      ";
@@ -5912,6 +5951,7 @@ static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
 		seq_printf(m, " %10lu%c", n, s[i]);
 	}
 	seq_putc(m, '\n');
+#endif
 }
 
 /* see Documentation/admin-guide/mm/multigen_lru.rst for details */
@@ -6186,6 +6226,9 @@ void lru_gen_init_lruvec(struct lruvec *lruvec)
 		INIT_LIST_HEAD(&lrugen->folios[gen][type][zone]);
 
 	lruvec->mm_state.seq = MIN_NR_GENS;
+#ifndef CONFIG_LRU_TASK_PAGE_AGING
+	spin_lock_init(&lruvec->mm_state.lock);
+#endif
 }
 
 #ifdef CONFIG_MEMCG
@@ -6202,6 +6245,7 @@ void lru_gen_init_pgdat(struct pglist_data *pgdat)
 	}
 }
 
+#ifdef CONFIG_LRU_TASK_PAGE_AGING
 void lru_gen_init_memcg(struct mem_cgroup *memcg)
 {
 	INIT_LIST_HEAD(&memcg->mm_list.fifo);
@@ -6229,6 +6273,7 @@ void lru_gen_exit_memcg(struct mem_cgroup *memcg)
 		}
 	}
 }
+#endif
 
 #endif /* CONFIG_MEMCG */
 
-- 
2.41.0