Message-Id: <1305276473-14780-13-git-send-email-gthelen@google.com>
Date:	Fri, 13 May 2011 01:47:51 -0700
From:	Greg Thelen <gthelen@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	containers@...ts.osdl.org, linux-fsdevel@...r.kernel.org,
	Andrea Righi <arighi@...eler.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Ciju Rajan K <ciju@...ux.vnet.ibm.com>,
	David Rientjes <rientjes@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Dave Chinner <david@...morbit.com>,
	Greg Thelen <gthelen@...gle.com>
Subject: [RFC][PATCH v7 12/14] memcg: create support routines for page-writeback

Introduce memcg routines to assist in per-memcg dirty page management:

- mem_cgroup_balance_dirty_pages() walks a memcg hierarchy comparing
  dirty memory usage against memcg foreground and background thresholds.
  If an over-background-threshold memcg is found, then per-memcg
  background writeback is queued.  If an over-foreground-threshold memcg
  is found, then foreground writeout occurs.  When performing foreground
  writeout, first consider inodes exclusive to the memcg.  If unable to
  make enough progress, then consider inodes shared between memcg.  Such
  cross-memcg inode sharing likely to be rare in situations that use
  per-cgroup memory isolation.  So the approach tries to handle the
  common case well without falling over in cases where such sharing
  exists.  This routine is used by balance_dirty_pages() in a later
  change.

- mem_cgroup_hierarchical_dirty_info() returns the dirty memory usage
  and limits of the memcg closest to (or over) its dirty limit.  This
  will be used by throttle_vm_writeout() in a latter change.

Signed-off-by: Greg Thelen <gthelen@...gle.com>
---
 include/linux/memcontrol.h        |   18 +++++
 include/trace/events/memcontrol.h |   83 ++++++++++++++++++++
 mm/memcontrol.c                   |  150 +++++++++++++++++++++++++++++++++++++
 3 files changed, 251 insertions(+), 0 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 3d72e09..0d0363e 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -167,6 +167,11 @@ bool should_writeback_mem_cgroup_inode(struct inode *inode,
 				       struct writeback_control *wbc);
 bool mem_cgroups_over_bground_dirty_thresh(void);
 void mem_cgroup_writeback_done(void);
+bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
+					struct mem_cgroup *mem,
+					struct dirty_info *info);
+void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
+				    unsigned long write_chunk);
 
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 						gfp_t gfp_mask,
@@ -383,6 +388,19 @@ static inline void mem_cgroup_writeback_done(void)
 {
 }
 
+static inline void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
+						  unsigned long write_chunk)
+{
+}
+
+static inline bool
+mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
+				   struct mem_cgroup *mem,
+				   struct dirty_info *info)
+{
+	return false;
+}
+
 static inline
 unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
 					    gfp_t gfp_mask,
diff --git a/include/trace/events/memcontrol.h b/include/trace/events/memcontrol.h
index 326a66b..b42dae1 100644
--- a/include/trace/events/memcontrol.h
+++ b/include/trace/events/memcontrol.h
@@ -109,6 +109,89 @@ TRACE_EVENT(mem_cgroups_over_bground_dirty_thresh,
 		  __entry->first_id)
 )
 
+DECLARE_EVENT_CLASS(mem_cgroup_consider_writeback,
+	TP_PROTO(unsigned short css_id,
+		 struct backing_dev_info *bdi,
+		 unsigned long nr_reclaimable,
+		 unsigned long thresh,
+		 bool over_limit),
+
+	TP_ARGS(css_id, bdi, nr_reclaimable, thresh, over_limit),
+
+	TP_STRUCT__entry(
+		__field(unsigned short, css_id)
+		__field(struct backing_dev_info *, bdi)
+		__field(unsigned long, nr_reclaimable)
+		__field(unsigned long, thresh)
+		__field(bool, over_limit)
+	),
+
+	TP_fast_assign(
+		__entry->css_id = css_id;
+		__entry->bdi = bdi;
+		__entry->nr_reclaimable = nr_reclaimable;
+		__entry->thresh = thresh;
+		__entry->over_limit = over_limit;
+	),
+
+	TP_printk("css_id=%d bdi=%p nr_reclaimable=%ld thresh=%ld "
+		  "over_limit=%d", __entry->css_id, __entry->bdi,
+		  __entry->nr_reclaimable, __entry->thresh, __entry->over_limit)
+)
+
+#define DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(name) \
+DEFINE_EVENT(mem_cgroup_consider_writeback, name, \
+	TP_PROTO(unsigned short id, \
+		 struct backing_dev_info *bdi, \
+		 unsigned long nr_reclaimable, \
+		 unsigned long thresh, \
+		 bool over_limit), \
+	TP_ARGS(id, bdi, nr_reclaimable, thresh, over_limit) \
+)
+
+DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_bg_writeback);
+DEFINE_MEM_CGROUP_CONSIDER_WRITEBACK_EVENT(mem_cgroup_consider_fg_writeback);
+
+TRACE_EVENT(mem_cgroup_fg_writeback,
+	TP_PROTO(unsigned long write_chunk,
+		 struct writeback_control *wbc),
+
+	TP_ARGS(write_chunk, wbc),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, write_chunk)
+		__field(long, wbc_to_write)
+		__field(bool, shared_inodes)
+	),
+
+	TP_fast_assign(
+		__entry->write_chunk = write_chunk;
+		__entry->wbc_to_write = wbc->nr_to_write;
+		__entry->shared_inodes = wbc->shared_inodes;
+	),
+
+	TP_printk("write_chunk=%ld nr_to_write=%ld shared_inodes=%d",
+		  __entry->write_chunk,
+		  __entry->wbc_to_write,
+		  __entry->shared_inodes)
+)
+
+TRACE_EVENT(mem_cgroup_enable_shared_writeback,
+	TP_PROTO(unsigned short css_id),
+
+	TP_ARGS(css_id),
+
+	TP_STRUCT__entry(
+		__field(unsigned short, css_id)
+		),
+
+	TP_fast_assign(
+		__entry->css_id = css_id;
+		),
+
+	TP_printk("enabling shared writeback for memcg %d", __entry->css_id)
+)
+
 #endif /* _TRACE_MEMCONTROL_H */
 
 /* This part must be outside protection */
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 230f0fb..e595514 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1619,6 +1619,156 @@ void mem_cgroup_writeback_done(void)
 	}
 }
 
+/*
+ * This routine must be called by processes which are generating dirty pages.
+ * It considers the dirty pages usage and thresholds of the current cgroup and
+ * (depending if hierarchical accounting is enabled) ancestral memcg.  If any of
+ * the considered memcg are over their background dirty limit, then background
+ * writeback is queued.  If any are over the foreground dirty limit then
+ * throttle the dirtying task while writing dirty data.  The per-memcg dirty
+ * limits check by this routine are distinct from either the per-system,
+ * per-bdi, or per-task limits considered by balance_dirty_pages().
+ */
+void mem_cgroup_balance_dirty_pages(struct address_space *mapping,
+				    unsigned long write_chunk)
+{
+	struct backing_dev_info *bdi = mapping->backing_dev_info;
+	struct mem_cgroup *mem;
+	struct mem_cgroup *ref_mem;
+	struct dirty_info info;
+	unsigned long nr_reclaimable;
+	unsigned long sys_available_mem;
+	unsigned long pause = 1;
+	unsigned short id;
+	bool over;
+	bool shared_inodes;
+
+	if (mem_cgroup_disabled())
+		return;
+
+	sys_available_mem = determine_dirtyable_memory();
+
+	/* reference the memcg so it is not deleted during this routine */
+	rcu_read_lock();
+	mem = mem_cgroup_from_task(current);
+	if (mem && mem_cgroup_is_root(mem))
+		mem = NULL;
+	if (mem)
+		css_get(&mem->css);
+	rcu_read_unlock();
+	ref_mem = mem;
+
+	/* balance entire ancestry of current's mem. */
+	for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) {
+		id = css_id(&mem->css);
+
+		/*
+		 * keep throttling and writing inode data so long as mem is over
+		 * its dirty limit.
+		 */
+		for (shared_inodes = false; ; ) {
+			struct writeback_control wbc = {
+				.sync_mode	= WB_SYNC_NONE,
+				.older_than_this = NULL,
+				.range_cyclic	= 1,
+				.for_cgroup	= 1,
+				.nr_to_write	= write_chunk,
+				.shared_inodes	= shared_inodes,
+			};
+
+			/*
+			 * if mem is under dirty limit, then break from
+			 * throttling loop.
+			 */
+			mem_cgroup_dirty_info(sys_available_mem, mem, &info);
+			nr_reclaimable = dirty_info_reclaimable(&info);
+			over = nr_reclaimable > info.dirty_thresh;
+			trace_mem_cgroup_consider_fg_writeback(
+				id, bdi, nr_reclaimable, info.dirty_thresh,
+				over);
+			if (!over)
+				break;
+
+			mem_cgroup_mark_over_bg_thresh(mem);
+			writeback_inodes_wb(&bdi->wb, &wbc);
+			trace_mem_cgroup_fg_writeback(write_chunk, &wbc);
+			/* if no progress, then consider shared inodes */
+			if ((wbc.nr_to_write == write_chunk) &&
+			    !shared_inodes) {
+				trace_mem_cgroup_enable_shared_writeback(id);
+				shared_inodes = true;
+			}
+
+			/*
+			 * Sleep up to 100ms to throttle writer and wait for
+			 * queued background I/O to complete.
+			 */
+			__set_current_state(TASK_UNINTERRUPTIBLE);
+			io_schedule_timeout(pause);
+			pause <<= 1;
+			if (pause > HZ / 10)
+				pause = HZ / 10;
+		}
+
+		/* if mem is over background limit, then queue bg writeback */
+		over = nr_reclaimable >= info.background_thresh;
+		trace_mem_cgroup_consider_bg_writeback(
+			id, bdi, nr_reclaimable, info.background_thresh,
+			over);
+		if (over)
+			mem_cgroup_queue_bg_writeback(mem, bdi);
+	}
+
+	if (ref_mem)
+		css_put(&ref_mem->css);
+}
+
+/*
+ * Return the dirty thresholds and usage for the mem (within the ancestral chain
+ * of @mem) closest to its dirty limit or the first memcg over its limit.
+ *
+ * The check is not stable because the usage and limits can change asynchronous
+ * to this routine.
+ */
+bool mem_cgroup_hierarchical_dirty_info(unsigned long sys_available_mem,
+					struct mem_cgroup *mem,
+					struct dirty_info *info)
+{
+	unsigned long usage;
+	struct dirty_info uninitialized_var(cur_info);
+
+	if (mem_cgroup_disabled())
+		return false;
+
+	info->nr_writeback = ULONG_MAX;  /* invalid initial value */
+
+	/* walk up hierarchy enabled parents */
+	for (; mem_cgroup_has_dirty_limit(mem); mem = parent_mem_cgroup(mem)) {
+		mem_cgroup_dirty_info(sys_available_mem, mem, &cur_info);
+		usage = dirty_info_reclaimable(&cur_info) +
+			cur_info.nr_writeback;
+
+		/* if over limit, stop searching */
+		if (usage >= cur_info.dirty_thresh) {
+			*info = cur_info;
+			break;
+		}
+
+		/*
+		 * Save dirty usage of mem closest to its limit if either:
+		 *     - mem is the first mem considered
+		 *     - mem dirty margin is smaller than last recorded one
+		 */
+		if ((info->nr_writeback == ULONG_MAX) ||
+		    (cur_info.dirty_thresh - usage) <
+		    (info->dirty_thresh -
+		     (dirty_info_reclaimable(info) + info->nr_writeback)))
+			*info = cur_info;
+	}
+
+	return info->nr_writeback != ULONG_MAX;
+}
+
 static void mem_cgroup_start_move(struct mem_cgroup *mem)
 {
 	int cpu;
-- 
1.7.3.1

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