[PATCH v6 01/10] Basic kernel memory functionality for the Memory Controller

[Glauber Costa]

This patch lays down the foundation for the kernel memory component
of the Memory Controller.

As of today, I am only laying down the following files:

 * memory.independent_kmem_limit
 * memory.kmem.limit_in_bytes (currently ignored)
 * memory.kmem.usage_in_bytes (always zero)

Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
Reviewed-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
CC: Paul Menage <paul@xxxxxxxxxxxxxx>
CC: Greg Thelen <gthelen@xxxxxxxxxx>
---
 Documentation/cgroups/memory.txt |   36 ++++++++++++-
 init/Kconfig                     |   14 +++++
 mm/memcontrol.c                  |  107 ++++++++++++++++++++++++++++++++++++--
 3 files changed, 150 insertions(+), 7 deletions(-)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 06eb6d9..bf00cd2 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -44,8 +44,9 @@ Features:
  - oom-killer disable knob and oom-notifier
  - Root cgroup has no limit controls.
 
- Kernel memory and Hugepages are not under control yet. We just manage
- pages on LRU. To add more controls, we have to take care of performance.
+ Hugepages is not under control yet. We just manage pages on LRU. To add more
+ controls, we have to take care of performance. Kernel memory support is work
+ in progress, and the current version provides basically functionality.
 
 Brief summary of control files.
 
@@ -56,8 +57,11 @@ Brief summary of control files.
 				 (See 5.5 for details)
  memory.memsw.usage_in_bytes	 # show current res_counter usage for memory+Swap
 				 (See 5.5 for details)
+ memory.kmem.usage_in_bytes	 # show current res_counter usage for kmem only.
+				 (See 2.7 for details)
  memory.limit_in_bytes		 # set/show limit of memory usage
  memory.memsw.limit_in_bytes	 # set/show limit of memory+Swap usage
+ memory.kmem.limit_in_bytes	 # if allowed, set/show limit of kernel memory
  memory.failcnt			 # show the number of memory usage hits limits
  memory.memsw.failcnt		 # show the number of memory+Swap hits limits
  memory.max_usage_in_bytes	 # show max memory usage recorded
@@ -72,6 +76,9 @@ Brief summary of control files.
  memory.oom_control		 # set/show oom controls.
  memory.numa_stat		 # show the number of memory usage per numa node
 
+ memory.independent_kmem_limit	 # select whether or not kernel memory limits are
+				   independent of user limits
+
 1. History
 
 The memory controller has a long history. A request for comments for the memory
@@ -255,6 +262,31 @@ When oom event notifier is registered, event will be delivered.
   per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
   zone->lru_lock, it has no lock of its own.
 
+2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
+
+ With the Kernel memory extension, the Memory Controller is able to limit
+the amount of kernel memory used by the system. Kernel memory is fundamentally
+different than user memory, since it can't be swapped out, which makes it
+possible to DoS the system by consuming too much of this precious resource.
+Kernel memory limits are not imposed for the root cgroup.
+
+Memory limits as specified by the standard Memory Controller may or may not
+take kernel memory into consideration. This is achieved through the file
+memory.independent_kmem_limit. A Value different than 0 will allow for kernel
+memory to be controlled separately.
+
+When kernel memory limits are not independent, the limit values set in
+memory.kmem files are ignored.
+
+Currently no soft limit is implemented for kernel memory. It is future work
+to trigger slab reclaim when those limits are reached.
+
+CAUTION: As of this writing, the kmem extention may prevent tasks from moving
+among cgroups. If a task has kmem accounting in a cgroup, the task cannot be
+moved until the kmem resource is released. Also, until the resource is fully
+released, the cgroup cannot be destroyed. So, please consider your use cases
+and set kmem extention config option carefully.
+
 3. User Interface
 
 0. Configuration
diff --git a/init/Kconfig b/init/Kconfig
index 31ba0fd..e4b6246 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -689,6 +689,20 @@ config CGROUP_MEM_RES_CTLR_SWAP_ENABLED
 	  For those who want to have the feature enabled by default should
 	  select this option (if, for some reason, they need to disable it
 	  then swapaccount=0 does the trick).
+config CGROUP_MEM_RES_CTLR_KMEM
+	bool "Memory Resource Controller Kernel Memory accounting (EXPERIMENTAL)"
+	depends on CGROUP_MEM_RES_CTLR && EXPERIMENTAL
+	default n
+	help
+	  The Kernel Memory extension for Memory Resource Controller can limit
+	  the amount of memory used by kernel objects in the system. Those are
+	  fundamentally different from the entities handled by the standard
+	  Memory Controller, which are page-based, and can be swapped. Users of
+	  the kmem extension can use it to guarantee that no group of processes
+	  will ever exhaust kernel resources alone.
+
+	  WARNING: The current experimental implementation does not allow a
+	  task to move among different cgroups with a kmem resource being held.
 
 config CGROUP_PERF
 	bool "Enable perf_event per-cpu per-container group (cgroup) monitoring"
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2d57555..1cb7daa 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -226,6 +226,10 @@ struct mem_cgroup {
 	 */
 	struct res_counter memsw;
 	/*
+	 * the counter to account for kmem usage.
+	 */
+	struct res_counter kmem;
+	/*
 	 * Per cgroup active and inactive list, similar to the
 	 * per zone LRU lists.
 	 */
@@ -276,6 +280,11 @@ struct mem_cgroup {
 	 */
 	unsigned long 	move_charge_at_immigrate;
 	/*
+	 * Should kernel memory limits be stabilished independently
+	 * from user memory ?
+	 */
+	int		kmem_independent_accounting;
+	/*
 	 * percpu counter.
 	 */
 	struct mem_cgroup_stat_cpu *stat;
@@ -343,9 +352,14 @@ enum charge_type {
 };
 
 /* for encoding cft->private value on file */
-#define _MEM			(0)
-#define _MEMSWAP		(1)
-#define _OOM_TYPE		(2)
+
+enum mem_type {
+	_MEM = 0,
+	_MEMSWAP,
+	_OOM_TYPE,
+	_KMEM,
+};
+
 #define MEMFILE_PRIVATE(x, val)	(((x) << 16) | (val))
 #define MEMFILE_TYPE(val)	(((val) >> 16) & 0xffff)
 #define MEMFILE_ATTR(val)	((val) & 0xffff)
@@ -3838,10 +3852,17 @@ static inline u64 mem_cgroup_usage(struct mem_cgroup *mem, bool swap)
 	u64 val;
 
 	if (!mem_cgroup_is_root(mem)) {
+		val = 0;
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+		if (!mem->kmem_independent_accounting)
+			val = res_counter_read_u64(&mem->kmem, RES_USAGE);
+#endif
 		if (!swap)
-			return res_counter_read_u64(&mem->res, RES_USAGE);
+			val += res_counter_read_u64(&mem->res, RES_USAGE);
 		else
-			return res_counter_read_u64(&mem->memsw, RES_USAGE);
+			val += res_counter_read_u64(&mem->memsw, RES_USAGE);
+
+		return val;
 	}
 
 	val = mem_cgroup_recursive_stat(mem, MEM_CGROUP_STAT_CACHE);
@@ -3874,6 +3895,11 @@ static u64 mem_cgroup_read(struct cgroup *cont, struct cftype *cft)
 		else
 			val = res_counter_read_u64(&mem->memsw, name);
 		break;
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+	case _KMEM:
+		val = res_counter_read_u64(&mem->kmem, name);
+		break;
+#endif
 	default:
 		BUG();
 		break;
@@ -4604,6 +4630,35 @@ static int mem_control_numa_stat_open(struct inode *unused, struct file *file)
 }
 #endif /* CONFIG_NUMA */
 
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+static u64 kmem_limit_independent_read(struct cgroup *cgroup, struct cftype *cft)
+{
+	return mem_cgroup_from_cont(cgroup)->kmem_independent_accounting;
+}
+
+static int kmem_limit_independent_write(struct cgroup *cgroup, struct cftype *cft,
+					u64 val)
+{
+	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
+	struct mem_cgroup *parent = parent_mem_cgroup(memcg);
+
+	val = !!val;
+
+	if (parent && parent->use_hierarchy &&
+	   (val != parent->kmem_independent_accounting))
+		return -EINVAL;
+	/*
+	 * TODO: We need to handle the case in which we are doing
+	 * independent kmem accounting as authorized by our parent,
+	 * but then our parent changes its parameter.
+	 */
+	cgroup_lock();
+	memcg->kmem_independent_accounting = val;
+	cgroup_unlock();
+	return 0;
+}
+#endif
+
 static struct cftype mem_cgroup_files[] = {
 	{
 		.name = "usage_in_bytes",
@@ -4719,6 +4774,42 @@ static int register_memsw_files(struct cgroup *cont, struct cgroup_subsys *ss)
 }
 #endif
 
+
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR_KMEM
+static struct cftype kmem_cgroup_files[] = {
+	{
+		.name = "independent_kmem_limit",
+		.read_u64 = kmem_limit_independent_read,
+		.write_u64 = kmem_limit_independent_write,
+	},
+	{
+		.name = "kmem.usage_in_bytes",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
+		.read_u64 = mem_cgroup_read,
+	},
+	{
+		.name = "kmem.limit_in_bytes",
+		.private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
+		.read_u64 = mem_cgroup_read,
+	},
+};
+
+static int register_kmem_files(struct cgroup *cont, struct cgroup_subsys *ss)
+{
+	int ret = 0;
+
+	ret = cgroup_add_files(cont, ss, kmem_cgroup_files,
+			       ARRAY_SIZE(kmem_cgroup_files));
+	return ret;
+};
+
+#else
+static int register_kmem_files(struct cgroup *cont, struct cgroup_subsys *ss)
+{
+	return 0;
+}
+#endif
+
 static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *mem, int node)
 {
 	struct mem_cgroup_per_node *pn;
@@ -4917,6 +5008,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	if (parent && parent->use_hierarchy) {
 		res_counter_init(&mem->res, &parent->res);
 		res_counter_init(&mem->memsw, &parent->memsw);
+		res_counter_init(&mem->kmem, &parent->kmem);
 		/*
 		 * We increment refcnt of the parent to ensure that we can
 		 * safely access it on res_counter_charge/uncharge.
@@ -4927,6 +5019,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	} else {
 		res_counter_init(&mem->res, NULL);
 		res_counter_init(&mem->memsw, NULL);
+		res_counter_init(&mem->kmem, NULL);
 	}
 	mem->last_scanned_child = 0;
 	mem->last_scanned_node = MAX_NUMNODES;
@@ -4970,6 +5063,10 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
 
 	if (!ret)
 		ret = register_memsw_files(cont, ss);
+
+	if (!ret)
+		ret = register_kmem_files(cont, ss);
+
 	return ret;
 }
 
-- 
1.7.6.4

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