linux-kernel - Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty

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Message-ID: <5242C960.7050506@hurleysoftware.com>
Date:	Wed, 25 Sep 2013 07:30:40 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Lin Ming <minggr@...il.com>
CC:	Fengguang Wu <fengguang.wu@...el.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	Tejun Heo <tj@...nel.org>
Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers
 into n_tty_data"

On 09/25/2013 05:04 AM, Lin Ming wrote:
> On Wed, Sep 18, 2013 at 8:22 AM, Peter Hurley <peter@...leysoftware.com> wrote:
> [snip]
>>
>> Looking over vmalloc.c, the critical section footprint of the vmap_area_lock
>> could definitely be reduced (even nearly eliminated), but that's a project
>> for
>> another day :)
>
> Hi Peter,
>
> I also looked over vmallo.c, but didn't find obvious way to reduce the
> critical section footprint.
> Could you share some hints how to do this?

vmap_area_list is an RCU list.
get_vmalloc_info() doesn't need to take the vmap_area_lock at all.
Look at __purge_vmap_area_lazy() for a howto.

Regards,
Peter Hurley

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