[lxc-devel] Swap Accounting :Query

[Serge Hallyn]

Quoting Nehal J Wani (nehaljw.kkd1 at gmail.com):
> I am using the most recent version of lxcfs, commit:
> 17f9a5a9d647467e3858fa751e40cc7c022dd475
> 
> When I spawn a container with the settings...
> 
> lxc.cgroup.memory.limit_in_bytes = 256M
> lxc.cgroup.memory.memsw.limit_in_bytes = 512M
> 
> ... I find that inside the container, we have:
> 
> [root at test ~]# free -m
>              total       used       free     shared    buffers     cached
> Mem:           256         24        231          6          0         20
> -/+ buffers/cache:          3        252
> Swap:         1023          0       1023
> 
> As you can see, the Total swap should have been 256MB, but it is being
> shown as ~1GB (same as host). Basically, my memsw setting is being
> ignored.
> 
> Now, when I revert the patch
> https://github.com/lxc/lxcfs/commit/a2de34bad72fb1b30af05d2f39a2b7bc6f20e42d
> 
> Then I see the correct usage:
> [root at test ~]# free -m
>              total       used       free     shared    buffers     cached
> Mem:           256         24        231          6          0         20
> -/+ buffers/cache:          3        252
> Swap:          256          0        256
> 
> But off course, this brings back the issue reported at
> https://github.com/lxc/lxcfs/issues/60
> 
> To fix both the problems, I proposed a patch at:
> https://lists.linuxcontainers.org/pipermail/lxc-devel/2016-January/013214.html
> which works well for me when host machine is CentOS 7. But fails to
> work when the host machine is Ubuntu 15.10
> 
> I followed:
> https://github.com/torvalds/linux/blob/v4.3/mm/memcontrol.c#L4037
> https://github.com/torvalds/linux/blob/v4.3/mm/memcontrol.c#L2893
> https://github.com/torvalds/linux/blob/v4.3/include/linux/page_counter.h#L21
> To find out that the default value for
> /sys/fs/cgroup/memory/lxc/test/memory.memsw.limit_in_bytes is
> RES_LIMIT, which is PAGE_COUNTER_MAX * PAGE_SIZE, which is equal to
> 9223372036854775807 (LONG_MAX) in case of CentOS7 (kernel 3.10.0) and
> 9223372036854771712 in case of Ubuntu14.04 (kernel 4.2.0). So
> assumption of LONG_MAX always is obviously wrong.
> 
> Only if somehow lxcfs knew that memsw.limit is not set in the
> container configuration...?

Can lxcfs just check that the value is the same for the queried cgroup
as for cgroup / ?