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

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 <redacted>
Reviewed-by: Kirill A. Shutemov <redacted>
CC: Paul Menage <redacted>
CC: Greg Thelen <redacted>
---
 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.
+