Re: [PATCH 1/2] Add mempressure cgroup

[Anton Vorontsov <anton.vorontsov@linaro.org>]

On Thu, Jan 10, 2013 at 01:20:30AM +0400, Glauber Costa wrote:
[...]
> Given the above, I believe that ideally we should use this pressure
> mechanism in memcg replacing the current memcg notification mechanism.

Just a quick wonder: why would we need to place it into memcg, when we
don't need any of the memcg stuff for it? I see no benefits, not
design-wise, not implementation-wise or anything-wise. :)

We can use mempressure w/o memcg, and even then it can (or should :) be
useful (for cpuset, for example).

> More or less like timer expiration happens: you could still write
> numbers for compatibility, but those numbers would be internally mapped
> into the levels Anton is proposing, that makes *way* more sense.
> 
> If that is not possible, they should coexist as "notification" and a
> "pressure" mechanism inside memcg.
> 
> The main argument against it centered around cpusets also being able to
> participate in the play. I haven't yet understood how would it take
> place. In particular, I saw no mention to cpusets in the patches.

I didn't test it, but as I see it, once a process in a specific cpuset,
the task can only use a specific allowed zones for reclaim/alloc, i.e.
various checks like this in vmscan:

         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
                     continue;

So, vmscan simply won't call vmpressure() if the zone is not allowed (so
we won't account that pressure, from that zone).

Thanks,
Anton

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