[PATCH v9 05/13] memcg: add mem_cgroup_mark_inode_dirty()

[Greg Thelen <gthelen@google.com>]

Create the mem_cgroup_mark_inode_dirty() routine, which is called when
an inode is marked dirty.  In kernels without memcg, this is an inline
no-op.

Add i_memcg field to struct address_space.  When an inode is marked
dirty with mem_cgroup_mark_inode_dirty(), the css_id of current memcg is
recorded in i_memcg.  Per-memcg writeback (introduced in a latter
change) uses this field to isolate inodes associated with a particular
memcg.

The type of i_memcg is an 'unsigned short' because it stores the css_id
of the memcg.  Using a struct mem_cgroup pointer would be larger and
also create a reference on the memcg which would hang memcg rmdir
deletion.  Usage of a css_id is not a reference so cgroup deletion is
not affected.  The memcg can be deleted without cleaning up the i_memcg
field.  When a memcg is deleted its pages are recharged to the cgroup
parent, and the related inode(s) are marked as shared thus
disassociating the inodes from the deleted cgroup.

A mem_cgroup_mark_inode_dirty() tracepoint is also included to allow for
easier understanding of memcg writeback operation.

Signed-off-by: Greg Thelen <gthelen@google.com>
---
Changelog since v8:
- Use I_MEMCG_SHARED when initializing i_memcg.

- Use 'memcg' rather than 'mem' for local variables.  This is consistent with
  other memory controller code.

- The logic in mem_cgroup_update_page_stat() and mem_cgroup_move_account() which
  marks inodes I_MEMCG_SHARED is now part of this patch.  This makes more sense
  because this is that patch that introduces that shared-inode concept.

 fs/fs-writeback.c                 |    2 +
 fs/inode.c                        |    3 ++
 include/linux/fs.h                |    9 +++++++
 include/linux/memcontrol.h        |    6 ++++
 include/trace/events/memcontrol.h |   32 +++++++++++++++++++++++++
 mm/memcontrol.c                   |   47 ++++++++++++++++++++++++++++++++++++-
 6 files changed, 98 insertions(+), 1 deletions(-)
 create mode 100644 include/trace/events/memcontrol.h

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 04cf3b9..6bf4c49 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -19,6 +19,7 @@
 #include <linux/slab.h>
 #include <linux/sched.h>
 #include <linux/fs.h>
+#include <linux/memcontrol.h>
 #include <linux/mm.h>
 #include <linux/kthread.h>
 #include <linux/freezer.h>
@@ -1111,6 +1112,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 			spin_lock(&bdi->wb.list_lock);
 			inode->dirtied_when = jiffies;
 			list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
+			mem_cgroup_mark_inode_dirty(inode);
 			spin_unlock(&bdi->wb.list_lock);
 
 			if (wakeup_bdi)
diff --git a/fs/inode.c b/fs/inode.c
index 5aab80d..87f0fcd 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -176,6 +176,9 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
 	mapping->assoc_mapping = NULL;
 	mapping->backing_dev_info = &default_backing_dev_info;
 	mapping->writeback_index = 0;
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	mapping->i_memcg = I_MEMCG_SHARED;
+#endif
 
 	/*
 	 * If the block_device provides a backing_dev_info for client
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0f496c2..417e9b93b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -651,6 +651,9 @@ struct address_space {
 	spinlock_t		private_lock;	/* for use by the address_space */
 	struct list_head	private_list;	/* ditto */
 	struct address_space	*assoc_mapping;	/* ditto */
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	unsigned short		i_memcg;	/* css_id of memcg dirtier */
+#endif
 } __attribute__((aligned(sizeof(long))));
 	/*
 	 * On most architectures that alignment is already the case; but
@@ -658,6 +661,12 @@ struct address_space {
 	 * of struct page's "mapping" pointer be used for PAGE_MAPPING_ANON.
 	 */
 
+/*
+ * When an address_space is shared by multiple memcg dirtieres, then i_memcg is
+ * set to this special, wildcard, css_id value (zero).
+ */
+#define I_MEMCG_SHARED 0
+
 struct block_device {
 	dev_t			bd_dev;  /* not a kdev_t - it's a search key */
 	int			bd_openers;
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index e6af3a9..630d3fa 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -119,6 +119,8 @@ mem_cgroup_prepare_migration(struct page *page,
 extern void mem_cgroup_end_migration(struct mem_cgroup *mem,
 	struct page *oldpage, struct page *newpage, bool migration_ok);
 
+void mem_cgroup_mark_inode_dirty(struct inode *inode);
+
 /*
  * For memory reclaim.
  */
@@ -297,6 +299,10 @@ static inline void mem_cgroup_end_migration(struct mem_cgroup *mem,
 {
 }
 
+static inline void mem_cgroup_mark_inode_dirty(struct inode *inode)
+{
+}
+
 static inline int mem_cgroup_get_reclaim_priority(struct mem_cgroup *mem)
 {
 	return 0;
diff --git a/include/trace/events/memcontrol.h b/include/trace/events/memcontrol.h
new file mode 100644
index 0000000..781ef9fc
--- /dev/null
+++ b/include/trace/events/memcontrol.h
@@ -0,0 +1,32 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM memcontrol
+
+#if !defined(_TRACE_MEMCONTROL_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MEMCONTROL_H
+
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(mem_cgroup_mark_inode_dirty,
+	TP_PROTO(struct inode *inode),
+
+	TP_ARGS(inode),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, ino)
+		__field(unsigned short, css_id)
+		),
+
+	TP_fast_assign(
+		__entry->ino = inode->i_ino;
+		__entry->css_id =
+			inode->i_mapping ? inode->i_mapping->i_memcg : 0;
+		),
+
+	TP_printk("ino=%ld css_id=%d", __entry->ino, __entry->css_id)
+)
+
+#endif /* _TRACE_MEMCONTROL_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 723b8bf..eda0d9a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -55,6 +55,9 @@
 
 #include <trace/events/vmscan.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/memcontrol.h>
+
 struct cgroup_subsys mem_cgroup_subsys __read_mostly;
 #define MEM_CGROUP_RECLAIM_RETRIES	5
 struct mem_cgroup *root_mem_cgroup __read_mostly;
@@ -1174,6 +1177,27 @@ static int calc_inactive_ratio(struct mem_cgroup *memcg, unsigned long *present_
 	return inactive_ratio;
 }
 
+/*
+ * Mark the current task's memcg as the memcg associated with inode.  Note: the
+ * recorded cgroup css_id is not guaranteed to remain correct.  The current task
+ * may be moved to another cgroup.  The memcg may also be deleted before the
+ * caller has time to use the i_memcg.
+ */
+void mem_cgroup_mark_inode_dirty(struct inode *inode)
+{
+	struct mem_cgroup *memcg;
+	unsigned short id;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_task(current);
+	id = memcg ? css_id(&memcg->css) : I_MEMCG_SHARED;
+	rcu_read_unlock();
+
+	inode->i_mapping->i_memcg = id;
+
+	trace_mem_cgroup_mark_inode_dirty(inode);
+}
+
 int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg)
 {
 	unsigned long active;
@@ -2041,6 +2065,7 @@ void mem_cgroup_update_page_stat(struct page *page,
 {
 	struct mem_cgroup *mem;
 	struct page_cgroup *pc = lookup_page_cgroup(page);
+	struct address_space *mapping;
 	bool need_unlock = false;
 	unsigned long uninitialized_var(flags);
 
@@ -2073,8 +2098,18 @@ void mem_cgroup_update_page_stat(struct page *page,
 	case MEMCG_NR_FILE_DIRTY:
 		/* Use Test{Set,Clear} to only un/charge the memcg once. */
 		if (val > 0) {
+			mapping = page_mapping(page);
 			if (TestSetPageCgroupFileDirty(pc))
 				val = 0;
+			else if (mapping &&
+				 (mapping->i_memcg != I_MEMCG_SHARED) &&
+				 (mapping->i_memcg != css_id(&mem->css)))
+				/*
+				 * If the inode is being dirtied by a memcg
+				 * other than the one that marked it dirty, then
+				 * mark the inode shared by multiple memcg.
+				 */
+				mapping->i_memcg = I_MEMCG_SHARED;
 		} else {
 			if (!TestClearPageCgroupFileDirty(pc))
 				val = 0;
@@ -2766,9 +2801,19 @@ static int mem_cgroup_move_account(struct page *page,
 	if (PageCgroupFileMapped(pc))
 		mem_cgroup_move_account_page_stat(from, to,
 					MEM_CGROUP_STAT_FILE_MAPPED);
-	if (PageCgroupFileDirty(pc))
+	if (PageCgroupFileDirty(pc)) {
 		mem_cgroup_move_account_page_stat(from, to,
 						  MEM_CGROUP_STAT_FILE_DIRTY);
+		/*
+		 * Moving a dirty file page between memcg makes the underlying
+		 * inode shared.  If the new (to) cgroup attempts writeback it
+		 * should consider this inode.  If the old (from) cgroup
+		 * attempts writeback it likely has other pages in the same
+		 * inode.  The inode is now shared by the to and from cgroups.
+		 * So mark the inode as shared.
+		 */
+		page_mapping(page)->i_memcg = I_MEMCG_SHARED;
+	}
 	if (PageCgroupFileWriteback(pc))
 		mem_cgroup_move_account_page_stat(from, to,
 					MEM_CGROUP_STAT_FILE_WRITEBACK);
-- 
1.7.3.1

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