Re: regression caused by cgroups optimization in 3.17-rc2

From: Dave Hansen
Date: Thu Sep 04 2014 - 16:50:41 EST

On 09/04/2014 08:08 AM, Johannes Weiner wrote:
> Dave Hansen reports a massive scalability regression in an uncontained
> page fault benchmark with more than 30 concurrent threads, which he
> bisected down to 05b843012335 ("mm: memcontrol: use root_mem_cgroup
> res_counter") and pin-pointed on res_counter spinlock contention.
> That change relied on the per-cpu charge caches to mostly swallow the
> res_counter costs, but it's apparent that the caches don't scale yet.
> Revert memcg back to bypassing res_counters on the root level in order
> to restore performance for uncontained workloads.

A quick sniff test shows performance coming back to what it was around
3.16 with this patch. I'll run a more thorough set of tests and verify
that it's working well.

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