On Mon 28-01-13 18:54:27, Jeff Liu wrote:

Hello,

Here is the v2 patch set for disabling swap_cgroup structures allocation
per swapon.

In the initial version, one big issue is that I have missed the swap tracking
for the root memcg, thanks Michal pointing it out. :)

In order to solve it, the easiest approach I can think out is to bypass the root
memcg swap accounting during the business and figure it out with some global stats,
which means that we always return 0 per root memcg swap charge/uncharge stage, and
this is inspired by another proposal from Zhengju:
"memcg: Don't account root memcg page statistics -- https://lkml.org/lkml/2013/1/2/71"

Besides that, another major fix is deallocate swap accounting structures on the last
non-root memcg remove after all references to it are gone rather than doing it on
mem_cgroup_destroy().

Any comment are welcome!

Could you also post your testing methodology and results, please? It
would be also really great if you could sum up memory savings.

Anyway thanks this second version looks really promising.

v1->v2:
- Refactor swap_cgroup_swapon()/swap_cgroup_prepare(), to make the later can be
  used for allocating buffers per the first non-root memcg creation.
- Bypass root memcg swap statistics, using the global stats to figure it out instead.
- Export nr_swap_files which would be used when creating/freeing swap_cgroup
- Deallocate swap accounting structures on the last non-root memcg removal

Old patch set:
v1:
http://marc.info/?l=linux-mm&m=135461016823964&w=2


Thanks,
-Jeff

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Michal Hocko
SUSE Labs