Re: [LSF/MM TOPIC] memory control groups

[Michel Lespinasse <walken@google.com>]

On Mon, Jan 17, 2011 at 11:14 AM, Johannes Weiner <hannes@cmpxchg.org> wrote:
> on the MM summit, I would like to talk about the current state of
> memory control groups, the features and extensions that are currently
> being developed for it, and what their status is.

+1 - there is a lot to discuss about memcg...

> I am especially interested in talking about the current runtime memory
> overhead memcg comes with (1% of ram) and what we can do to shrink it.
>
> In comparison to how efficiently struct page is packed, and given that
> distro kernels come with memcg enabled per default, I think we should
> put a bit more thought into how struct page_cgroup (which exists for
> every page in the system as well) is organized.
>
> I have a patch series that removes the page backpointer from struct
> page_cgroup by storing a node ID (or section ID, depending on whether
> sparsemem is configured) in the free bits of pc->flags.
>
> I also plan on replacing the pc->mem_cgroup pointer with an ID
> (KAMEZAWA-san has patches for that), and move it to pc->flags too.
> Every flag not used means doubling the amount of possible control
> groups, so I have patches that get rid of some flags currently
> allocated, including PCG_CACHE, PCG_ACCT_LRU, and PCG_MIGRATION.
>
> [ I meant to send those out much earlier already, but a bug in the
> migration rework was not responding to my yelling 'Marco', and now my
> changes collide horribly with THP, so it will take another rebase. ]
>
> The per-memcg dirty accounting work e.g. allocates a bunch of new bits
> in pc->flags and I'd like to hash out if this leaves enough room for
> the structure packing I described, or whether we can come up with a
> different way of tracking state.

This is probably longer term, but I would love to get rid of the
duplication between global LRU and per-cgroup LRU. Global LRU could be
approximated by scanning all per-cgroup LRU lists (in mounts
proportional to the list lengths).

> Would other people be interested in discussing this?

Definitely.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>