linux-kernel - Re: regression caused by cgroups optimization in 3.17-rc2

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Message-ID: <5408ED7A.5010908@intel.com>
Date:	Thu, 04 Sep 2014 15:53:46 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Dave Hansen <dave@...1.net>, Michal Hocko <mhocko@...e.cz>
CC:	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>, Tejun Heo <tj@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: regression caused by cgroups optimization in 3.17-rc2

On 09/04/2014 01:27 PM, Dave Hansen wrote:
> On 09/04/2014 07:27 AM, Michal Hocko wrote:
>> Ouch. free_pages_and_swap_cache completely kills the uncharge batching
>> because it reduces it to PAGEVEC_SIZE batches.
>>
>> I think we really do not need PAGEVEC_SIZE batching anymore. We are
>> already batching on tlb_gather layer. That one is limited so I think
>> the below should be safe but I have to think about this some more. There
>> is a risk of prolonged lru_lock wait times but the number of pages is
>> limited to 10k and the heavy work is done outside of the lock. If this
>> is really a problem then we can tear LRU part and the actual
>> freeing/uncharging into a separate functions in this path.
>>
>> Could you test with this half baked patch, please? I didn't get to test
>> it myself unfortunately.
> 
> 3.16 settled out at about 11.5M faults/sec before the regression.  This
> patch gets it back up to about 10.5M, which is good.  The top spinlock
> contention in the kernel is still from the resource counter code via
> mem_cgroup_commit_charge(), though.
> 
> I'm running Johannes' patch now.

This looks pretty good.  The area where it plateaus (above 80 threads
where hyperthreading kicks in) might be a bit slower than it was in
3.16, but that could easily be from other things.

> https://www.sr71.net/~dave/intel/bb.html?1=3.16.0-rc4-g67b9d76/&2=3.17.0-rc3-g57b252f

Feel free to add my Tested-by:

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