[patch 4/4] memcg: use native word page statistics counters

[Johannes Weiner <hannes@cmpxchg.org>]

[-- Attachment #1: memcg-use-native-word-page-statistics-counters.patch --]
[-- Type: text/plain, Size: 5024 bytes --]

The statistic counters are in units of pages, there is no reason to
make them 64-bit wide on 32-bit machines.

Make them native words.  Since they are signed, this leaves 31 bit on
32-bit machines, which can represent roughly 8TB assuming a page size
of 4k.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/memcontrol.h |    2 +-
 mm/memcontrol.c            |   43 +++++++++++++++++++++----------------------
 mm/page-writeback.c        |    4 ++--
 3 files changed, 24 insertions(+), 25 deletions(-)

--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -110,7 +110,7 @@ enum {
 };
 
 struct mem_cgroup_stat_cpu {
-	s64 count[MEM_CGROUP_STAT_NSTATS];
+	long count[MEM_CGROUP_STAT_NSTATS];
 	unsigned long events[MEM_CGROUP_EVENTS_NSTATS];
 };
 
@@ -583,11 +583,11 @@ mem_cgroup_largest_soft_limit_node(struc
  * common workload, threashold and synchonization as vmstat[] should be
  * implemented.
  */
-static s64 mem_cgroup_read_stat(struct mem_cgroup *mem,
-		enum mem_cgroup_stat_index idx)
+static long mem_cgroup_read_stat(struct mem_cgroup *mem,
+				 enum mem_cgroup_stat_index idx)
 {
+	long val = 0;
 	int cpu;
-	s64 val = 0;
 
 	for_each_online_cpu(cpu)
 		val += per_cpu(mem->stat->count[idx], cpu);
@@ -599,9 +599,9 @@ static s64 mem_cgroup_read_stat(struct m
 	return val;
 }
 
-static s64 mem_cgroup_local_usage(struct mem_cgroup *mem)
+static long mem_cgroup_local_usage(struct mem_cgroup *mem)
 {
-	s64 ret;
+	long ret;
 
 	ret = mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_RSS);
 	ret += mem_cgroup_read_stat(mem, MEM_CGROUP_STAT_CACHE);
@@ -1244,7 +1244,7 @@ bool mem_cgroup_dirty_info(unsigned long
 	struct vm_dirty_param dirty_param;
 	unsigned long available_mem;
 	struct mem_cgroup *memcg;
-	s64 value;
+	long value;
 
 	if (mem_cgroup_disabled())
 		return false;
@@ -1301,10 +1301,10 @@ static inline bool mem_cgroup_can_swap(s
 		(res_counter_read_u64(&memcg->memsw, RES_LIMIT) > 0);
 }
 
-static s64 mem_cgroup_local_page_stat(struct mem_cgroup *mem,
-				      enum mem_cgroup_nr_pages_item item)
+static long mem_cgroup_local_page_stat(struct mem_cgroup *mem,
+				       enum mem_cgroup_nr_pages_item item)
 {
-	s64 ret;
+	long ret;
 
 	switch (item) {
 	case MEMCG_NR_DIRTYABLE_PAGES:
@@ -1365,11 +1365,11 @@ memcg_hierarchical_free_pages(struct mem
  * Return the accounted statistic value or negative value if current task is
  * root cgroup.
  */
-s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
+long mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item)
 {
-	struct mem_cgroup *mem;
 	struct mem_cgroup *iter;
-	s64 value;
+	struct mem_cgroup *mem;
+	long value;
 
 	get_online_cpus();
 	rcu_read_lock();
@@ -2069,7 +2069,7 @@ static void mem_cgroup_drain_pcp_counter
 
 	spin_lock(&mem->pcp_counter_lock);
 	for (i = 0; i < MEM_CGROUP_STAT_DATA; i++) {
-		s64 x = per_cpu(mem->stat->count[i], cpu);
+		long x = per_cpu(mem->stat->count[i], cpu);
 
 		per_cpu(mem->stat->count[i], cpu) = 0;
 		mem->nocpu_base.count[i] += x;
@@ -3660,13 +3660,13 @@ static int mem_cgroup_hierarchy_write(st
 }
 
 
-static u64 mem_cgroup_get_recursive_idx_stat(struct mem_cgroup *mem,
-				enum mem_cgroup_stat_index idx)
+static unsigned long mem_cgroup_recursive_stat(struct mem_cgroup *mem,
+					       enum mem_cgroup_stat_index idx)
 {
 	struct mem_cgroup *iter;
-	s64 val = 0;
+	long val = 0;
 
-	/* each per cpu's value can be minus.Then, use s64 */
+	/* Per-cpu values can be negative, use a signed accumulator */
 	for_each_mem_cgroup_tree(iter, mem)
 		val += mem_cgroup_read_stat(iter, idx);
 
@@ -3686,12 +3686,11 @@ static inline u64 mem_cgroup_usage(struc
 			return res_counter_read_u64(&mem->memsw, RES_USAGE);
 	}
 
-	val = mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_CACHE);
-	val += mem_cgroup_get_recursive_idx_stat(mem, MEM_CGROUP_STAT_RSS);
+	val = mem_cgroup_recursive_stat(mem, MEM_CGROUP_STAT_CACHE);
+	val += mem_cgroup_recursive_stat(mem, MEM_CGROUP_STAT_RSS);
 
 	if (swap)
-		val += mem_cgroup_get_recursive_idx_stat(mem,
-				MEM_CGROUP_STAT_SWAPOUT);
+		val += mem_cgroup_recursive_stat(mem, MEM_CGROUP_STAT_SWAPOUT);
 
 	return val << PAGE_SHIFT;
 }
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -157,7 +157,7 @@ static inline void mem_cgroup_dec_page_s
 bool mem_cgroup_has_dirty_limit(void);
 bool mem_cgroup_dirty_info(unsigned long sys_available_mem,
 			   struct dirty_info *info);
-s64 mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item);
+long mem_cgroup_page_stat(enum mem_cgroup_nr_pages_item item);
 
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask);
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -133,10 +133,10 @@ static struct prop_descriptor vm_dirties
 
 static unsigned long dirty_writeback_pages(void)
 {
-	s64 ret;
+	unsigned long ret;
 
 	ret = mem_cgroup_page_stat(MEMCG_NR_DIRTY_WRITEBACK_PAGES);
-	if (ret < 0)
+	if ((long)ret < 0)
 		ret = global_page_state(NR_UNSTABLE_NFS) +
 			global_page_state(NR_WRITEBACK);