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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <540DCF99.2070900@intel.com>
Date:	Mon, 08 Sep 2014 08:47:37 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Johannes Weiner <hannes@...xchg.org>, Dave Hansen <dave@...1.net>
CC:	Michal Hocko <mhocko@...e.cz>, 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 09/05/2014 05:35 AM, Johannes Weiner wrote:
> 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?

I don't have the perf output that I was looking at when I said this, but
here's the path that I think I was referring to.  The inlining makes
this non-obvious, but this memcg_check_events() calls
mem_cgroup_update_tree() which is contending on mctz->lock.

So, you were right, it's not the resource counters code, it's a lock in
'struct mem_cgroup_tree_per_zone'.  But, the contention isn't _that_
high (2% of CPU) in this case.  But, that is 2% that we didn't see before.

>      1.87%     1.87%  [kernel]               [k] _raw_spin_lock_irqsave       
>                                |
>                                --- _raw_spin_lock_irqsave
>                                   |          
>                                   |--107.09%-- memcg_check_events
>                                   |          |          
>                                   |          |--79.98%-- mem_cgroup_commit_charge
>                                   |          |          |          
>                                   |          |          |--99.81%-- do_cow_fault
>                                   |          |          |          handle_mm_fault
>                                   |          |          |          __do_page_fault
>                                   |          |          |          do_page_fault
>                                   |          |          |          page_fault
>                                   |          |          |          testcase
>                                   |          |           --0.19%-- [...]


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/