Memory Resource Controller
-NOTE: The Memory Resource Controller has been generically been referred
- to as the memory controller in this document. Do not confuse memory
- controller used here with the memory controller that is used in hardware.
+NOTE: The Memory Resource Controller has generically been referred to as the
+ memory controller in this document. Do not confuse memory controller
+ used here with the memory controller that is used in hardware.
(For editors)
In this document:
tasks # attach a task(thread) and show list of threads
cgroup.procs # show list of processes
cgroup.event_control # an interface for event_fd()
- memory.usage_in_bytes # show current memory(RSS+Cache) usage.
- memory.memsw.usage_in_bytes # show current memory+Swap usage
+ memory.usage_in_bytes # show current res_counter usage for memory
+ (See 5.5 for details)
+ memory.memsw.usage_in_bytes # show current res_counter usage for memory+Swap
+ (See 5.5 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.failcnt # show the number of memory usage hits limits
(See sysctl's vm.swappiness)
memory.move_charge_at_immigrate # set/show controls of moving charges
memory.oom_control # set/show oom controls.
+ memory.numa_stat # show the number of memory usage per numa node
1. History
page will eventually get charged for it (once it is uncharged from
the cgroup that brought it in -- this will happen on memory pressure).
-Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used..
+Exception: If CONFIG_CGROUP_CGROUP_MEM_RES_CTLR_SWAP is not used.
When you do swapoff and make swapped-out pages of shmem(tmpfs) to
be backed into memory in force, charges for pages are accounted against the
caller of swapoff rather than the users of shmem.
OS point of view.
* What happens when a cgroup hits memory.memsw.limit_in_bytes
-When a cgroup his memory.memsw.limit_in_bytes, it's useless to do swap-out
+When a cgroup hits memory.memsw.limit_in_bytes, it's useless to do swap-out
in this cgroup. Then, swap-out will not be done by cgroup routine and file
caches are dropped. But as mentioned above, global LRU can do swapout memory
from it for sanity of the system's memory management state. You can't forbid
c. Enable CONFIG_CGROUP_MEM_RES_CTLR
d. Enable CONFIG_CGROUP_MEM_RES_CTLR_SWAP (to use swap extension)
-1. Prepare the cgroups
-# mkdir -p /cgroups
-# mount -t cgroup none /cgroups -o memory
+1. Prepare the cgroups (see cgroups.txt, Why are cgroups needed?)
+# mount -t tmpfs none /sys/fs/cgroup
+# mkdir /sys/fs/cgroup/memory
+# mount -t cgroup none /sys/fs/cgroup/memory -o memory
2. Make the new group and move bash into it
-# mkdir /cgroups/0
-# echo $$ > /cgroups/0/tasks
+# mkdir /sys/fs/cgroup/memory/0
+# echo $$ > /sys/fs/cgroup/memory/0/tasks
Since now we're in the 0 cgroup, we can alter the memory limit:
-# echo 4M > /cgroups/0/memory.limit_in_bytes
+# echo 4M > /sys/fs/cgroup/memory/0/memory.limit_in_bytes
NOTE: We can use a suffix (k, K, m, M, g or G) to indicate values in kilo,
mega or gigabytes. (Here, Kilo, Mega, Giga are Kibibytes, Mebibytes, Gibibytes.)
NOTE: We can write "-1" to reset the *.limit_in_bytes(unlimited).
NOTE: We cannot set limits on the root cgroup any more.
-# cat /cgroups/0/memory.limit_in_bytes
+# cat /sys/fs/cgroup/memory/0/memory.limit_in_bytes
4194304
We can check the usage:
-# cat /cgroups/0/memory.usage_in_bytes
+# cat /sys/fs/cgroup/memory/0/memory.usage_in_bytes
1216512
A successful write to this file does not guarantee a successful set of
You can reset failcnt by writing 0 to failcnt file.
# echo 0 > .../memory.failcnt
+5.5 usage_in_bytes
+
+For efficiency, as other kernel components, memory cgroup uses some optimization
+to avoid unnecessary cacheline false sharing. usage_in_bytes is affected by the
+method and doesn't show 'exact' value of memory(and swap) usage, it's an fuzz
+value for efficient access. (Of course, when necessary, it's synchronized.)
+If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
+value in memory.stat(see 5.2).
+
+5.6 numa_stat
+
+This is similar to numa_maps but operates on a per-memcg basis. This is
+useful for providing visibility into the numa locality information within
+an memcg since the pages are allowed to be allocated from any physical
+node. One of the usecases is evaluating application performance by
+combining this information with the application's cpu allocation.
+
+We export "total", "file", "anon" and "unevictable" pages per-node for
+each memcg. The ouput format of memory.numa_stat is:
+
+total=<total pages> N0=<node 0 pages> N1=<node 1 pages> ...
+file=<total file pages> N0=<node 0 pages> N1=<node 1 pages> ...
+anon=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ...
+unevictable=<total anon pages> N0=<node 0 pages> N1=<node 1 pages> ...
+
+And we have total = file + anon + unevictable.
+
6. Hierarchy support
The memory controller supports a deep hierarchy and hierarchical accounting.
cgroup filesystem. Consider for example, the following cgroup filesystem
hierarchy
- root
+ root
/ | \
- / | \
- a b c
- | \
- | \
- d e
+ / | \
+ a b c
+ | \
+ | \
+ d e
In the diagram above, with hierarchical accounting enabled, all memory
usage of e, is accounted to its ancestors up until the root (i.e, c and root),
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