[RFC][preview] [patch 1/2] memcg: batched uncharge base

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

In massive parallel enviroment, res_counter can be a performance bottleneck.
This patch is a trial for reducing lock contention in memcg.

One strong techinque to reduce lock contention is reducing calls themselves by
do some amount of calls into a call, in batch.

Considering charge/uncharge chatacteristic,
	- charge is done one by one via demand-paging.
	- uncharge is done by
		- in continuous call at munmap, truncate, exit, execve...
		- one by one via vmscan/paging.

It seems we have a chance to batched-uncharge.
This patch is a base patch for batched uncharge. For avoiding
scattering memcg's structure as argument, this patch adds memcg batch uncharge
information to the task. please see start/end usage in next patch.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
 include/linux/memcontrol.h |   12 ++++++++++
 include/linux/sched.h      |    8 +++++++
 mm/memcontrol.c            |   51 ++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 68 insertions(+), 3 deletions(-)

Index: linux-2.6.31-rc7/include/linux/memcontrol.h
===================================================================
--- linux-2.6.31-rc7.orig/include/linux/memcontrol.h
+++ linux-2.6.31-rc7/include/linux/memcontrol.h
@@ -54,6 +54,10 @@ extern void mem_cgroup_rotate_lru_list(s
 extern void mem_cgroup_del_lru(struct page *page);
 extern void mem_cgroup_move_lists(struct page *page,
 				  enum lru_list from, enum lru_list to);
+
+extern void mem_cgroup_uncharge_batch_start(void);
+extern void mem_cgroup_uncharge_batch_end(void);
+
 extern void mem_cgroup_uncharge_page(struct page *page);
 extern void mem_cgroup_uncharge_cache_page(struct page *page);
 extern int mem_cgroup_shmem_charge_fallback(struct page *page,
@@ -148,6 +152,14 @@ static inline void mem_cgroup_cancel_cha
 {
 }
 
+static inline void mem_cgroup_uncharge_batch_start(void)
+{
+}
+
+static inline void mem_cgroup_uncharge_batch_start(void)
+{
+}
+
 static inline void mem_cgroup_uncharge_page(struct page *page)
 {
 }
Index: linux-2.6.31-rc7/mm/memcontrol.c
===================================================================
--- linux-2.6.31-rc7.orig/mm/memcontrol.c
+++ linux-2.6.31-rc7/mm/memcontrol.c
@@ -1500,6 +1500,7 @@ __mem_cgroup_uncharge_common(struct page
 	struct page_cgroup *pc;
 	struct mem_cgroup *mem = NULL;
 	struct mem_cgroup_per_zone *mz;
+	struct memcg_batch_info *batch = NULL;
 
 	if (mem_cgroup_disabled())
 		return NULL;
@@ -1537,10 +1538,25 @@ __mem_cgroup_uncharge_common(struct page
 	default:
 		break;
 	}
+	if (current->batch_memcg.batch_mode)
+		batch = &current->batch_memcg;
 
-	res_counter_uncharge(&mem->res, PAGE_SIZE);
-	if (do_swap_account && (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
-		res_counter_uncharge(&mem->memsw, PAGE_SIZE);
+	if (!batch || batch->memcg != mem) {
+		res_counter_uncharge(&mem->res, PAGE_SIZE);
+		if (do_swap_account &&
+		    (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
+			res_counter_uncharge(&mem->memsw, PAGE_SIZE);
+		if (batch) {
+			batch->memcg = mem;
+			css_get(&mem->css);
+		}
+	} else {
+		/* instead of modifing res_counter, remember it */
+		batch->nr_pages += PAGE_SIZE;
+		if (do_swap_account &&
+		    (ctype != MEM_CGROUP_CHARGE_TYPE_SWAPOUT))
+			batch->nr_memsw += PAGE_SIZE;
+	}
 	mem_cgroup_charge_statistics(mem, pc, false);
 
 	ClearPageCgroupUsed(pc);
@@ -1582,6 +1598,35 @@ void mem_cgroup_uncharge_cache_page(stru
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_CACHE);
 }
 
+void mem_cgroup_uncharge_batch_start(void)
+{
+	VM_BUG_ON(current->batch_memcg.batch_mode);
+	current->batch_memcg.batch_mode = 1;
+	current->batch_memcg.memcg = NULL;
+	current->batch_memcg.nr_pages = 0;
+	current->batch_memcg.nr_memsw = 0;
+}
+
+void mem_cgroup_uncharge_batch_end(void)
+{
+	struct mem_cgroup *mem;
+
+	VM_BUG_ON(!current->batch_memcg.batch_mode);
+	current->batch_memcg.batch_mode = 0;
+
+	mem = current->batch_memcg.memcg;
+	if (!mem)
+		return;
+	if (current->batch_memcg.nr_pages)
+		res_counter_uncharge(&mem->res,
+				     current->batch_memcg.nr_pages);
+	if (current->batch_memcg.nr_memsw)
+		res_counter_uncharge(&mem->memsw,
+				     current->batch_memcg.nr_memsw);
+	/* we got css's refcnt */
+	cgroup_release_and_wakeup_rmdir(&mem->css);
+}
+
 #ifdef CONFIG_SWAP
 /*
  * called after __delete_from_swap_cache() and drop "page" account.
Index: linux-2.6.31-rc7/include/linux/sched.h
===================================================================
--- linux-2.6.31-rc7.orig/include/linux/sched.h
+++ linux-2.6.31-rc7/include/linux/sched.h
@@ -1480,6 +1480,14 @@ struct task_struct {
 	/* bitmask of trace recursion */
 	unsigned long trace_recursion;
 #endif /* CONFIG_TRACING */
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	/* For implicit argument for batched uncharge */
+	struct memcg_batch_info {
+		struct mem_cgroup *memcg;
+		int batch_mode;
+		unsigned long nr_pages, nr_memsw;
+	} batch_memcg;
+#endif
 };
 
 /* Future-safe accessor for struct task_struct's cpus_allowed. */

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