From: Peter Hurley <peter@hurleysoftware.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
lkp@01.org, Tejun Heo <tj@kernel.org>
Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"
Date: Fri, 13 Sep 2013 05:55:47 -0400 [thread overview]
Message-ID: <5232E123.9090909@hurleysoftware.com> (raw)
In-Reply-To: <20130913034413.GA26166@kroah.com>
On 09/12/2013 11:44 PM, Greg KH wrote:
> On Fri, Sep 13, 2013 at 11:38:04AM +0800, Fengguang Wu wrote:
>> On Thu, Sep 12, 2013 at 08:17:00PM -0700, Greg KH wrote:
>>> On Fri, Sep 13, 2013 at 08:51:33AM +0800, Fengguang Wu wrote:
>>>> Hi Peter,
>>>>
>>>> FYI, we noticed much increased vmap_area_lock contentions since this
>>>> commit:
>>>
>>> What does that mean? What is happening, are we allocating/removing more
>>> memory now?
No. Same amount of memory, allocated and freed with the same frequency as
before.
>>> What type of load were you running that showed this problem?
>>
>> The increased contentions and lock hold/wait time showed up in a
>> number of test cases.
[...]
> That's a lot of slowdowns, especially for such a simple patch.
>
> Peter, any ideas?
Looks like this patch incidentally triggers some worst-case behavior in
the memory manager. I'm not sure how this is possible with two 4k buffers,
but the evidence is substantial.
This patch isn't critical so I suggest we back out this patch for mainline
but use the patch to find out what's wrong in the vmap area.
Unfortunately, I'm on my way out the door and won't be back til Sunday pm (EST)
so I'll get a revert to you then. Sorry 'bout that.
Regards,
Peter Hurley
next prev parent reply other threads:[~2013-09-13 9:55 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-13 0:51 increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" Fengguang Wu
2013-09-13 1:09 ` Fengguang Wu
2013-09-17 15:34 ` Peter Hurley
2013-09-17 23:22 ` Fengguang Wu
2013-09-18 0:22 ` Peter Hurley
2013-09-25 9:04 ` Lin Ming
2013-09-25 11:30 ` Peter Hurley
2013-09-25 14:53 ` Lin Ming
2013-09-25 16:02 ` Lin Ming
2013-09-26 3:20 ` Andi Kleen
2013-09-26 11:52 ` Peter Hurley
2013-09-26 15:32 ` Andi Kleen
2013-09-26 17:22 ` Peter Hurley
2013-09-26 7:33 ` Andrew Morton
2013-09-26 11:31 ` Peter Hurley
2013-09-26 15:04 ` Greg KH
2013-09-26 17:35 ` Peter Hurley
2013-09-26 18:05 ` Andrew Morton
2013-09-26 21:42 ` Peter Hurley
2013-09-26 21:58 ` Andrew Morton
2013-09-26 22:21 ` Peter Hurley
2013-09-18 0:49 ` Peter Hurley
2013-09-13 3:17 ` Greg KH
2013-09-13 3:38 ` Fengguang Wu
2013-09-13 3:44 ` Greg KH
2013-09-13 9:55 ` Peter Hurley [this message]
2013-09-13 12:34 ` Greg KH
2013-09-17 2:42 ` Peter Hurley
2013-09-17 2:56 ` Fengguang Wu
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