[PATCH v3 02/19] mm: memcg: prepare for byte-sized vmstat items

[Roman Gushchin <guro@fb.com>]

To implement per-object slab memory accounting, we need to
convert slab vmstat counters to bytes. Actually, out of
4 levels of counters: global, per-node, per-memcg and per-lruvec
only two last levels will require byte-sized counters.
It's because global and per-node counters will be counting the
number of slab pages, and per-memcg and per-lruvec will be
counting the amount of memory taken by charged slab objects.

Converting all vmstat counters to bytes or even all slab
counters to bytes would introduce an additional overhead.
So instead let's store global and per-node counters
in pages, and memcg and lruvec counters in bytes.

To make the API clean all access helpers (both on the read
and write sides) are dealing with bytes.

To avoid back-and-forth conversions a new flavor of helpers
is introduced, which always returns values in pages:
node_page_state_pages() and global_node_page_state_pages().

Actually new helpers are just reading raw values. Old helpers are
simple wrappers, which perform a conversion if the vmstat items are
in bytes. Because at the moment no one actually need bytes,
there are WARN_ON_ONCE() macroses inside to warn about inappropriate
use cases.

Thanks to Johannes Weiner for the idea of having the byte-sized API
on top of the page-sized internal storage.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
 drivers/base/node.c    |  2 +-
 include/linux/mmzone.h |  5 +++++
 include/linux/vmstat.h | 16 +++++++++++++++-
 mm/memcontrol.c        | 14 ++++++++++----
 mm/vmstat.c            | 33 +++++++++++++++++++++++++++++----
 5 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/drivers/base/node.c b/drivers/base/node.c
index 10d7e818e118..9d6afb7d2ccd 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -507,7 +507,7 @@ static ssize_t node_read_vmstat(struct device *dev,
 
 	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
 		n += sprintf(buf+n, "%s %lu\n", node_stat_name(i),
-			     node_page_state(pgdat, i));
+			     node_page_state_pages(pgdat, i));
 
 	return n;
 }
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index c1fbda9ddd1f..22fe65edf425 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -204,6 +204,11 @@ enum node_stat_item {
 	NR_VM_NODE_STAT_ITEMS
 };
 
+static __always_inline bool vmstat_item_in_bytes(enum node_stat_item item)
+{
+	return false;
+}
+
 /*
  * We do arithmetic on the LRU lists in various places in the code,
  * so it is important to keep the active lists LRU_ACTIVE higher in
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 292485f3d24d..117763827cd0 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -190,7 +190,8 @@ static inline unsigned long global_zone_page_state(enum zone_stat_item item)
 	return x;
 }
 
-static inline unsigned long global_node_page_state(enum node_stat_item item)
+static inline
+unsigned long global_node_page_state_pages(enum node_stat_item item)
 {
 	long x = atomic_long_read(&vm_node_stat[item]);
 #ifdef CONFIG_SMP
@@ -200,6 +201,16 @@ static inline unsigned long global_node_page_state(enum node_stat_item item)
 	return x;
 }
 
+static inline unsigned long global_node_page_state(enum node_stat_item item)
+{
+	unsigned long x = global_node_page_state_pages(item);
+
+	if (WARN_ON_ONCE(vmstat_item_in_bytes(item)))
+		return x << PAGE_SHIFT;
+
+	return x;
+}
+
 static inline unsigned long zone_page_state(struct zone *zone,
 					enum zone_stat_item item)
 {
@@ -240,9 +251,12 @@ extern unsigned long sum_zone_node_page_state(int node,
 extern unsigned long sum_zone_numa_state(int node, enum numa_stat_item item);
 extern unsigned long node_page_state(struct pglist_data *pgdat,
 						enum node_stat_item item);
+extern unsigned long node_page_state_pages(struct pglist_data *pgdat,
+					   enum node_stat_item item);
 #else
 #define sum_zone_node_page_state(node, item) global_zone_page_state(item)
 #define node_page_state(node, item) global_node_page_state(item)
+#define node_page_state_pages(node, item) global_node_page_state_pages(item)
 #endif /* CONFIG_NUMA */
 
 #ifdef CONFIG_SMP
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f6ff20095105..5f700fa8b78c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -681,13 +681,16 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_node *mctz)
  */
 void __mod_memcg_state(struct mem_cgroup *memcg, int idx, int val)
 {
-	long x;
+	long x, threshold = MEMCG_CHARGE_BATCH;
 
 	if (mem_cgroup_disabled())
 		return;
 
+	if (vmstat_item_in_bytes(idx))
+		threshold <<= PAGE_SHIFT;
+
 	x = val + __this_cpu_read(memcg->vmstats_percpu->stat[idx]);
-	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+	if (unlikely(abs(x) > threshold)) {
 		struct mem_cgroup *mi;
 
 		/*
@@ -719,7 +722,7 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 	pg_data_t *pgdat = lruvec_pgdat(lruvec);
 	struct mem_cgroup_per_node *pn;
 	struct mem_cgroup *memcg;
-	long x;
+	long x, threshold = MEMCG_CHARGE_BATCH;
 
 	pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
 	memcg = pn->memcg;
@@ -730,8 +733,11 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx,
 	/* Update lruvec */
 	__this_cpu_add(pn->lruvec_stat_local->count[idx], val);
 
+	if (vmstat_item_in_bytes(idx))
+		threshold <<= PAGE_SHIFT;
+
 	x = val + __this_cpu_read(pn->lruvec_stat_cpu->count[idx]);
-	if (unlikely(abs(x) > MEMCG_CHARGE_BATCH)) {
+	if (unlikely(abs(x) > threshold)) {
 		struct mem_cgroup_per_node *pi;
 
 		for (pi = pn; pi; pi = parent_nodeinfo(pi, pgdat->node_id))
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 6fd1407f4632..7ac13f6d189a 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -341,6 +341,11 @@ void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item,
 	long x;
 	long t;
 
+	if (vmstat_item_in_bytes(item)) {
+		WARN_ON(delta & (PAGE_SIZE - 1));
+		delta >>= PAGE_SHIFT;
+	}
+
 	x = delta + __this_cpu_read(*p);
 
 	t = __this_cpu_read(pcp->stat_threshold);
@@ -398,6 +403,8 @@ void __inc_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 	s8 __percpu *p = pcp->vm_node_stat_diff + item;
 	s8 v, t;
 
+	WARN_ON_ONCE(vmstat_item_in_bytes(item));
+
 	v = __this_cpu_inc_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v > t)) {
@@ -442,6 +449,8 @@ void __dec_node_state(struct pglist_data *pgdat, enum node_stat_item item)
 	s8 __percpu *p = pcp->vm_node_stat_diff + item;
 	s8 v, t;
 
+	WARN_ON_ONCE(vmstat_item_in_bytes(item));
+
 	v = __this_cpu_dec_return(*p);
 	t = __this_cpu_read(pcp->stat_threshold);
 	if (unlikely(v < - t)) {
@@ -541,6 +550,11 @@ static inline void mod_node_state(struct pglist_data *pgdat,
 	s8 __percpu *p = pcp->vm_node_stat_diff + item;
 	long o, n, t, z;
 
+	if (vmstat_item_in_bytes(item)) {
+		WARN_ON_ONCE(delta & (PAGE_SIZE - 1));
+		delta >>= PAGE_SHIFT;
+	}
+
 	do {
 		z = 0;  /* overflow to node counters */
 
@@ -989,8 +1003,8 @@ unsigned long sum_zone_numa_state(int node,
 /*
  * Determine the per node value of a stat item.
  */
-unsigned long node_page_state(struct pglist_data *pgdat,
-				enum node_stat_item item)
+unsigned long node_page_state_pages(struct pglist_data *pgdat,
+				    enum node_stat_item item)
 {
 	long x = atomic_long_read(&pgdat->vm_stat[item]);
 #ifdef CONFIG_SMP
@@ -999,6 +1013,17 @@ unsigned long node_page_state(struct pglist_data *pgdat,
 #endif
 	return x;
 }
+
+unsigned long node_page_state(struct pglist_data *pgdat,
+				enum node_stat_item item)
+{
+	unsigned long x = node_page_state_pages(pgdat, item);
+
+	if (WARN_ON_ONCE(vmstat_item_in_bytes(item)))
+		return x << PAGE_SHIFT;
+
+	return x;
+}
 #endif
 
 #ifdef CONFIG_COMPACTION
@@ -1571,7 +1596,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		seq_printf(m, "\n  per-node stats");
 		for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) {
 			seq_printf(m, "\n      %-12s %lu", node_stat_name(i),
-				   node_page_state(pgdat, i));
+				   node_page_state_pages(pgdat, i));
 		}
 	}
 	seq_printf(m,
@@ -1692,7 +1717,7 @@ static void *vmstat_start(struct seq_file *m, loff_t *pos)
 #endif
 
 	for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++)
-		v[i] = global_node_page_state(i);
+		v[i] = global_node_page_state_pages(i);
 	v += NR_VM_NODE_STAT_ITEMS;
 
 	global_dirty_limits(v + NR_DIRTY_BG_THRESHOLD,
-- 
2.25.3