[Devel] Re: [RFC PATCH 0/5] memcg: VM overcommit accounting and handling

[KAMEZAWA Hiroyuki]

On Tue, 10 Jun 2008 01:32:58 +0200
Andrea Righi <righi.andrea at gmail.com> wrote:

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

Could you explain the benefits of this even when we have memrlimit controller ?
(If unsure, see 2.6.26-rc5-mm1 and search memrlimit controller.)

And this kind of virtual-address-handling things should be implemented on
memrlimit controller (means not on memory-resource-controller.).
It seems this patch doesn't need to handle page_group.

Considering hierarchy, putting several kinds of features on one controller is
not good, I think. Balbir, how do you think ?

Thanks,
-Kame


> 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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