Re: [mm] 42a3003535: will-it-scale.per_process_ops -25.9% regression

[Johannes Weiner]

Hello,

On Mon, May 20, 2019 at 02:35:34PM +0800, kernel test robot wrote:
> Greeting,
> 
> FYI, we noticed a -25.9% regression of will-it-scale.per_process_ops due to commit:
> 
> 
> commit: 42a300353577ccc17ecc627b8570a89fa1678bec ("mm: memcontrol: fix recursive statistics correctness & scalabilty")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: will-it-scale
> on test machine: 192 threads Skylake-SP with 256G memory
> with following parameters:

Ouch. That has to be the additional cache footprint of the split
local/recursive stat counters, rather than the extra instructions.

Could you please try re-running the test on that host with the below
patch applied?

Also CCing Aaron Lu, who has previously investigated the cache layout
in the struct memcg stat counters.

> 	nr_task: 100%
> 	mode: process
> 	test: page_fault3
> 	cpufreq_governor: performance