[PATCH v2 14/16] mm: multigenerational lru: user interface

[Yu Zhao <yuzhao@google.com>]

Add a sysfs file /sys/kernel/mm/lru_gen/enabled so users can enable
and disable the multigenerational lru at runtime.

Add a sysfs file /sys/kernel/mm/lru_gen/spread so users can spread
pages out across multiple generations. More generations make the
background aging more aggressive.

Add a debugfs file /sys/kernel/debug/lru_gen so users can monitor the
multigenerational lru and trigger the aging and the eviction. This
file has the following output:
  memcg  memcg_id  memcg_path
    node  node_id
      min_gen  birth_time  anon_size  file_size
      ...
      max_gen  birth_time  anon_size  file_size

Given a memcg and a node, "min_gen" is the oldest generation (number)
and "max_gen" is the youngest. Birth time is in milliseconds. The
sizes of anon and file types are in pages.

This file takes the following input:
  + memcg_id node_id gen [swappiness]
  - memcg_id node_id gen [swappiness] [nr_to_reclaim]

The first command line accounts referenced pages to generation
"max_gen" and creates the next generation "max_gen"+1. In this case,
"gen" should be equal to "max_gen". A swap file and a non-zero
"swappiness" are required to scan anon type. If swapping is not
desired, set vm.swappiness to 0. The second command line evicts
generations less than or equal to "gen". In this case, "gen" should be
less than "max_gen"-1 as "max_gen" and "max_gen"-1 are active
generations and therefore protected from the eviction. Use
"nr_to_reclaim" to limit the number of pages to be evicted. Multiple
command lines are supported, so does concatenation with delimiters ","
and ";".

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 mm/vmscan.c | 405 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 405 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 01c475386379..284e32d897cf 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -51,6 +51,8 @@
 #include <linux/psi.h>
 #include <linux/memory.h>
 #include <linux/pagewalk.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -6248,6 +6250,403 @@ static int __meminit __maybe_unused lru_gen_online_mem(struct notifier_block *se
 	return NOTIFY_DONE;
 }
 
+/******************************************************************************
+ *                          sysfs interface
+ ******************************************************************************/
+
+static ssize_t show_lru_gen_spread(struct kobject *kobj, struct kobj_attribute *attr,
+				   char *buf)
+{
+	return sprintf(buf, "%d\n", READ_ONCE(lru_gen_spread));
+}
+
+static ssize_t store_lru_gen_spread(struct kobject *kobj, struct kobj_attribute *attr,
+				    const char *buf, size_t len)
+{
+	int spread;
+
+	if (kstrtoint(buf, 10, &spread) || spread >= MAX_NR_GENS)
+		return -EINVAL;
+
+	WRITE_ONCE(lru_gen_spread, spread);
+
+	return len;
+}
+
+static struct kobj_attribute lru_gen_spread_attr = __ATTR(
+	spread, 0644, show_lru_gen_spread, store_lru_gen_spread
+);
+
+static ssize_t show_lru_gen_enabled(struct kobject *kobj, struct kobj_attribute *attr,
+				    char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%ld\n", lru_gen_enabled());
+}
+
+static ssize_t store_lru_gen_enabled(struct kobject *kobj, struct kobj_attribute *attr,
+				     const char *buf, size_t len)
+{
+	int enable;
+
+	if (kstrtoint(buf, 10, &enable))
+		return -EINVAL;
+
+	lru_gen_set_state(enable, true, false);
+
+	return len;
+}
+
+static struct kobj_attribute lru_gen_enabled_attr = __ATTR(
+	enabled, 0644, show_lru_gen_enabled, store_lru_gen_enabled
+);
+
+static struct attribute *lru_gen_attrs[] = {
+	&lru_gen_spread_attr.attr,
+	&lru_gen_enabled_attr.attr,
+	NULL
+};
+
+static struct attribute_group lru_gen_attr_group = {
+	.name = "lru_gen",
+	.attrs = lru_gen_attrs,
+};
+
+/******************************************************************************
+ *                          debugfs interface
+ ******************************************************************************/
+
+static void *lru_gen_seq_start(struct seq_file *m, loff_t *pos)
+{
+	struct mem_cgroup *memcg;
+	loff_t nr_to_skip = *pos;
+
+	m->private = kzalloc(PATH_MAX, GFP_KERNEL);
+	if (!m->private)
+		return ERR_PTR(-ENOMEM);
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		int nid;
+
+		for_each_node_state(nid, N_MEMORY) {
+			if (!nr_to_skip--)
+				return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+
+	return NULL;
+}
+
+static void lru_gen_seq_stop(struct seq_file *m, void *v)
+{
+	if (!IS_ERR_OR_NULL(v))
+		mem_cgroup_iter_break(NULL, lruvec_memcg(v));
+
+	kfree(m->private);
+	m->private = NULL;
+}
+
+static void *lru_gen_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	int nid = lruvec_pgdat(v)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(v);
+
+	++*pos;
+
+	nid = next_memory_node(nid);
+	if (nid == MAX_NUMNODES) {
+		memcg = mem_cgroup_iter(NULL, memcg, NULL);
+		if (!memcg)
+			return NULL;
+
+		nid = first_memory_node;
+	}
+
+	return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+}
+
+static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
+				  unsigned long max_seq, unsigned long *min_seq,
+				  unsigned long seq)
+{
+	int i;
+	int file, tier;
+	int sid = sid_from_seq_or_gen(seq);
+	struct lrugen *lrugen = &lruvec->evictable;
+	int nid = lruvec_pgdat(lruvec)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
+
+	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
+		seq_printf(m, "            %10d", tier);
+		for (file = 0; file < ANON_AND_FILE; file++) {
+			unsigned long n[3] = {};
+
+			if (seq == max_seq) {
+				n[0] = READ_ONCE(lrugen->avg_refaulted[file][tier]);
+				n[1] = READ_ONCE(lrugen->avg_total[file][tier]);
+
+				seq_printf(m, " %10luR %10luT %10lu ", n[0], n[1], n[2]);
+			} else if (seq == min_seq[file] || NR_STAT_GENS > 1) {
+				n[0] = atomic_long_read(&lrugen->refaulted[sid][file][tier]);
+				n[1] = atomic_long_read(&lrugen->evicted[sid][file][tier]);
+				if (tier)
+					n[2] = READ_ONCE(lrugen->activated[sid][file][tier - 1]);
+
+				seq_printf(m, " %10lur %10lue %10lua", n[0], n[1], n[2]);
+			} else
+				seq_puts(m, "          0           0           0 ");
+		}
+		seq_putc(m, '\n');
+	}
+
+	seq_puts(m, "                      ");
+	for (i = 0; i < NR_MM_STATS; i++) {
+		if (seq == max_seq && NR_STAT_GENS == 1)
+			seq_printf(m, " %10lu%c", READ_ONCE(mm_list->nodes[nid].stats[sid][i]),
+				   toupper(MM_STAT_CODES[i]));
+		else if (seq != max_seq && NR_STAT_GENS > 1)
+			seq_printf(m, " %10lu%c", READ_ONCE(mm_list->nodes[nid].stats[sid][i]),
+				   MM_STAT_CODES[i]);
+		else
+			seq_puts(m, "          0 ");
+	}
+	seq_putc(m, '\n');
+}
+
+static int lru_gen_seq_show(struct seq_file *m, void *v)
+{
+	unsigned long seq;
+	bool full = !debugfs_real_fops(m->file)->write;
+	struct lruvec *lruvec = v;
+	struct lrugen *lrugen = &lruvec->evictable;
+	int nid = lruvec_pgdat(lruvec)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	DEFINE_MAX_SEQ();
+	DEFINE_MIN_SEQ();
+
+	if (nid == first_memory_node) {
+#ifdef CONFIG_MEMCG
+		if (memcg)
+			cgroup_path(memcg->css.cgroup, m->private, PATH_MAX);
+#endif
+		seq_printf(m, "memcg %5hu %s\n",
+			   mem_cgroup_id(memcg), (char *)m->private);
+	}
+
+	seq_printf(m, " node %5d %10d\n", nid, atomic_read(&lrugen->priority));
+
+	seq = full ? (max_seq < MAX_NR_GENS ? 0 : max_seq - MAX_NR_GENS + 1) :
+		     min(min_seq[0], min_seq[1]);
+
+	for (; seq <= max_seq; seq++) {
+		int gen, file, zone;
+		unsigned int msecs;
+
+		gen = lru_gen_from_seq(seq);
+		msecs = jiffies_to_msecs(jiffies - READ_ONCE(lrugen->timestamps[gen]));
+
+		seq_printf(m, " %10lu %10u", seq, msecs);
+
+		for (file = 0; file < ANON_AND_FILE; file++) {
+			long size = 0;
+
+			if (seq < min_seq[file]) {
+				seq_puts(m, "         -0 ");
+				continue;
+			}
+
+			for (zone = 0; zone < MAX_NR_ZONES; zone++)
+				size += READ_ONCE(lrugen->sizes[gen][file][zone]);
+
+			seq_printf(m, " %10lu ", max(size, 0L));
+		}
+
+		seq_putc(m, '\n');
+
+		if (full)
+			lru_gen_seq_show_full(m, lruvec, max_seq, min_seq, seq);
+	}
+
+	return 0;
+}
+
+static const struct seq_operations lru_gen_seq_ops = {
+	.start = lru_gen_seq_start,
+	.stop = lru_gen_seq_stop,
+	.next = lru_gen_seq_next,
+	.show = lru_gen_seq_show,
+};
+
+static int advance_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness)
+{
+	struct mm_walk_args args = {};
+	struct scan_control sc = {
+		.target_mem_cgroup = lruvec_memcg(lruvec),
+	};
+	DEFINE_MAX_SEQ();
+
+	if (seq == max_seq)
+		walk_mm_list(lruvec, max_seq, &sc, swappiness, &args);
+
+	return seq > max_seq ? -EINVAL : 0;
+}
+
+static int advance_min_seq(struct lruvec *lruvec, unsigned long seq, int swappiness,
+			   unsigned long nr_to_reclaim)
+{
+	struct blk_plug plug;
+	int err = -EINTR;
+	long nr_to_scan = LONG_MAX;
+	struct scan_control sc = {
+		.nr_to_reclaim = nr_to_reclaim,
+		.target_mem_cgroup = lruvec_memcg(lruvec),
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+		.reclaim_idx = MAX_NR_ZONES - 1,
+		.gfp_mask = GFP_KERNEL,
+	};
+	DEFINE_MAX_SEQ();
+
+	if (seq >= max_seq - 1)
+		return -EINVAL;
+
+	blk_start_plug(&plug);
+
+	while (!signal_pending(current)) {
+		DEFINE_MIN_SEQ();
+
+		if (seq < min(min_seq[!swappiness], min_seq[swappiness < 200]) ||
+		    !evict_lru_gen_pages(lruvec, &sc, swappiness, &nr_to_scan)) {
+			err = 0;
+			break;
+		}
+
+		cond_resched();
+	}
+
+	blk_finish_plug(&plug);
+
+	return err;
+}
+
+static int advance_seq(char cmd, int memcg_id, int nid, unsigned long seq,
+		       int swappiness, unsigned long nr_to_reclaim)
+{
+	struct lruvec *lruvec;
+	int err = -EINVAL;
+	struct mem_cgroup *memcg = NULL;
+
+	if (!mem_cgroup_disabled()) {
+		rcu_read_lock();
+		memcg = mem_cgroup_from_id(memcg_id);
+#ifdef CONFIG_MEMCG
+		if (memcg && !css_tryget(&memcg->css))
+			memcg = NULL;
+#endif
+		rcu_read_unlock();
+
+		if (!memcg)
+			goto done;
+	}
+	if (memcg_id != mem_cgroup_id(memcg))
+		goto done;
+
+	if (nid < 0 || nid >= MAX_NUMNODES || !node_state(nid, N_MEMORY))
+		goto done;
+
+	lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+
+	if (swappiness == -1)
+		swappiness = get_swappiness(lruvec);
+	else if (swappiness > 200U)
+		goto done;
+
+	switch (cmd) {
+	case '+':
+		err = advance_max_seq(lruvec, seq, swappiness);
+		break;
+	case '-':
+		err = advance_min_seq(lruvec, seq, swappiness, nr_to_reclaim);
+		break;
+	}
+done:
+	mem_cgroup_put(memcg);
+
+	return err;
+}
+
+static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
+				 size_t len, loff_t *pos)
+{
+	void *buf;
+	char *cur, *next;
+	int err = 0;
+
+	buf = kvmalloc(len + 1, GFP_USER);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, src, len)) {
+		kvfree(buf);
+		return -EFAULT;
+	}
+
+	next = buf;
+	next[len] = '\0';
+
+	while ((cur = strsep(&next, ",;\n"))) {
+		int n;
+		int end;
+		char cmd;
+		int memcg_id;
+		int nid;
+		unsigned long seq;
+		int swappiness = -1;
+		unsigned long nr_to_reclaim = -1;
+
+		cur = skip_spaces(cur);
+		if (!*cur)
+			continue;
+
+		n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
+			   &seq, &end, &swappiness, &end, &nr_to_reclaim, &end);
+		if (n < 4 || cur[end]) {
+			err = -EINVAL;
+			break;
+		}
+
+		err = advance_seq(cmd, memcg_id, nid, seq, swappiness, nr_to_reclaim);
+		if (err)
+			break;
+	}
+
+	kvfree(buf);
+
+	return err ? : len;
+}
+
+static int lru_gen_seq_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &lru_gen_seq_ops);
+}
+
+static const struct file_operations lru_gen_rw_fops = {
+	.open = lru_gen_seq_open,
+	.read = seq_read,
+	.write = lru_gen_seq_write,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+static const struct file_operations lru_gen_ro_fops = {
+	.open = lru_gen_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
 /******************************************************************************
  *                          initialization
  ******************************************************************************/
@@ -6291,6 +6690,12 @@ static int __init init_lru_gen(void)
 	if (hotplug_memory_notifier(lru_gen_online_mem, 0))
 		pr_err("lru_gen: failed to subscribe hotplug notifications\n");
 
+	if (sysfs_create_group(mm_kobj, &lru_gen_attr_group))
+		pr_err("lru_gen: failed to create sysfs group\n");
+
+	debugfs_create_file("lru_gen", 0644, NULL, NULL, &lru_gen_rw_fops);
+	debugfs_create_file("lru_gen_full", 0444, NULL, NULL, &lru_gen_ro_fops);
+
 	return 0;
 };
 /*
-- 
2.31.1.295.g9ea45b61b8-goog