Hi Glauber,

On Tue, Feb 21, 2012 at 3:34 AM, Glauber Costa [off-list ref] wrote:

This is a first structured approach to tracking general kernel
memory within the memory controller. Please tell me what you think.

Thanks for posting these.

As previously proposed, one has the option of keeping kernel memory
accounted separatedly, or together with the normal userspace memory.
However, this time I made the option to, in this later case, bill
the memory directly to memcg->res. It has the disadvantage that it becomes
complicated to know which memory came from user or kernel, but OTOH,
it does not create any overhead of drawing from multiple res_counters
at read time. (and if you want them to be joined, you probably don't care)

It would be nice to still keep a kernel memory counter (that gets
updated at the same time as memcg->res) even when the limits are not
independent, because sometimes it's important to know how much kernel
memory is being used by a cgroup.

Kernel memory is never tracked for the root memory cgroup. This means
that a system where no memory cgroups exists other than the root, the
time cost of this implementation is a couple of branches in the slub
code - none of them in fast paths. At the moment, this works only
with the slub.

At cgroup destruction, memory is billed to the parent. With no hierarchy,
this would mean the root memcg. But since we are not billing to that,
it simply ceases to be tracked.

The caches that we want to be tracked need to explicit register into
the infrastructure.

Why not track every cache unless otherwise specified? If you don't,
you might end up polluting code all around the kernel to create
per-cgroup caches.

From what I've seen, there are a fair amount of different caches that

can end up using a significant amount of memory, and having to go
around and explicitly mark each one doesn't seem like the right thing
to do.

-- Suleiman

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