core: add cgroup memory controller support on the unified hierarchy (#3315)

On the unified hierarchy, memory controller implements three control knobs -
low, high and max which enables more useable and versatile control over memory
usage.  This patch implements support for the three control knobs.

* MemoryLow, MemoryHigh and MemoryMax are added for memory.low, memory.high and
  memory.max, respectively.

* As all absolute limits on the unified hierarchy use "max" for no limit, make
  memory limit parse functions accept "max" in addition to "infinity" and
  document "max" for the new knobs.

* Implement compatibility translation between MemoryMax and MemoryLimit.

v2:

- Fixed missing else's in config_parse_memory_limit().
- Fixed missing newline when writing out drop-ins.
- Coding style updates to use "val > 0" instead of "val".
- Minor updates to documentation.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/core/cgroup.h b/src/core/cgroup.h
index 2a9e7034a..68cb65007 100644
--- a/src/core/cgroup.h
+++ b/src/core/cgroup.h
@@ -95,6 +95,10 @@ struct CGroupContext {
         LIST_HEAD(CGroupIODeviceWeight, io_device_weights);
         LIST_HEAD(CGroupIODeviceLimit, io_device_limits);
 
+        uint64_t memory_low;
+        uint64_t memory_high;
+        uint64_t memory_max;
+
         /* For legacy hierarchies */
         uint64_t cpu_shares;
         uint64_t startup_cpu_shares;