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

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Date:	Fri, 5 Sep 2014 08:35:17 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Dave Hansen <dave@...1.net>
Cc:	Michal Hocko <mhocko@...e.cz>, Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.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 Thu, Sep 04, 2014 at 01:27:26PM -0700, 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.

Thanks for testing, that looks a lot better.

But commit doesn't touch resource counters - did you mean try_charge()
or uncharge() by any chance?

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