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Subject[RFC PATCH 0/5] memcg: VM overcommit accounting and handling
Date

Provide distinct cgroup VM overcommit accounting and handling using the memory
resource controller.

Patchset against latest Linus git tree.

This patchset allows to set different per-cgroup overcommit rules and,
according to them, it's possible to return a memory allocation failure (ENOMEM)
to the applications, instead of always triggering the OOM killer via
mem_cgroup_out_of_memory() when cgroup memory limits are exceeded.

Default overcommit settings are taken from vm.overcommit_memory and
vm.overcommit_ratio sysctl values. Child cgroups initially inherits the VM
overcommit parent's settings.

Cgroup overcommit settings can be overridden using memory.overcommit_memory and
memory.overcommit_ratio files under the cgroup filesystem.

For example:

1. Initialize a cgroup with 50MB memory limit:
# mount -t cgroup none /cgroups -o memory
# mkdir /cgroups/0
# /bin/echo $$ > /cgroups/0/tasks
# /bin/echo 50M > /cgroups/0/memory.limit_in_bytes

2. Use the "never overcommit" policy with 50% ratio:
# /bin/echo 2 > /cgroups/0/memory.overcommit_memory
# /bin/echo 50 > /cgroups/0/memory.overcommit_ratio

Assuming we have no swap space, cgroup 0 can allocate up to 25MB of virtual
memory. If that limit is exceeded all the further allocation attempts made by
userspace applications will receive a -ENOMEM.

4. Show committed VM statistics:
# cat /cgroups/0/memory.overcommit_as
CommitLimit: 25600 kB
Committed_AS: 9844 kB

5. Use "always overcommmit":
# /bin/echo 1 > /cgroups/0/memory.overcommit_memory

This is very similar to the default memory controller configuration: overcommit
is allowed, but when there's no more available memory oom-killer is invoked.

TODO:
- shared memory is not taken in account (i.e. files in tmpfs)

-Andrea


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