Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756083Ab3IYQCn (ORCPT ); Wed, 25 Sep 2013 12:02:43 -0400 Received: from mail-pd0-f172.google.com ([209.85.192.172]:34550 "EHLO mail-pd0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755443Ab3IYQCm (ORCPT ); Wed, 25 Sep 2013 12:02:42 -0400 Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" From: Lin Ming To: Peter Hurley Cc: Fengguang Wu , Greg KH , LKML , lkp@01.org, Tejun Heo In-Reply-To: <5242C960.7050506@hurleysoftware.com> References: <20130913005133.GA32479@localhost> <20130913010936.GA1291@localhost> <5238767D.1080606@hurleysoftware.com> <20130917232214.GA11390@localhost> <5238F252.5070905@hurleysoftware.com> <5242C960.7050506@hurleysoftware.com> Content-Type: text/plain; charset="ISO-8859-1" Date: Thu, 26 Sep 2013 00:02:24 +0800 Message-ID: <1380124944.27676.1.camel@monkey32> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2150 Lines: 81 On Wed, 2013-09-25 at 07:30 -0400, Peter Hurley wrote: > On 09/25/2013 05:04 AM, Lin Ming wrote: > > On Wed, Sep 18, 2013 at 8:22 AM, Peter Hurley 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. Would you like below patch? From: Lin Ming Date: Wed, 25 Sep 2013 23:48:19 +0800 Subject: [PATCH] mm/vmalloc.c: eliminate vmap_area_lock in get_vmalloc_info() vmap_area_list is an RCU list. get_vmalloc_info() doesn't need to take the vmap_area_lock at all. Use RCU to protect list scan. Signed-off-by: Lin Ming --- mm/vmalloc.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 13a5495..4523c9c 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2684,14 +2684,14 @@ void get_vmalloc_info(struct vmalloc_info *vmi) prev_end = VMALLOC_START; - spin_lock(&vmap_area_lock); + rcu_read_lock(); if (list_empty(&vmap_area_list)) { vmi->largest_chunk = VMALLOC_TOTAL; goto out; } - list_for_each_entry(va, &vmap_area_list, list) { + list_for_each_entry_rcu(va, &vmap_area_list, list) { unsigned long addr = va->va_start; /* @@ -2718,7 +2718,7 @@ void get_vmalloc_info(struct vmalloc_info *vmi) vmi->largest_chunk = VMALLOC_END - prev_end; out: - spin_unlock(&vmap_area_lock); + rcu_read_unlock(); } #endif -- 1.7.2.5 > > Regards, > Peter Hurley > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/