From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932994Ab0BDAW6 (ORCPT ); Wed, 3 Feb 2010 19:22:58 -0500 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:50106 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932096Ab0BDAW5 convert rfc822-to-8bit (ORCPT ); Wed, 3 Feb 2010 19:22:57 -0500 X-SecurityPolicyCheck-FJ: OK by FujitsuOutboundMailChecker v1.3.1 From: KOSAKI Motohiro To: John Kacur Subject: Re: [RFC][PATCH] vmscan: balance local_irq_disable() and local_irq_enable() Cc: kosaki.motohiro@jp.fujitsu.com, rostedt@goodmis.org, lkml , Thomas Gleixner , Ingo Molnar , Andrew Morton , Rik van Riel , Johannes Weiner , Minchan Kim , linux-mm@kvack.org In-Reply-To: <520f0cf11002031212p4f1497e3he82dce3af668e676@mail.gmail.com> References: <1265227746.24386.15.camel@gandalf.stny.rr.com> <520f0cf11002031212p4f1497e3he82dce3af668e676@mail.gmail.com> Message-Id: <20100204091938.C2C6.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8BIT X-Mailer: Becky! ver. 2.50.07 [ja] Date: Thu, 4 Feb 2010 09:22:54 +0900 (JST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Wed, Feb 3, 2010 at 9:09 PM, Steven Rostedt wrote: > > t On Wed, 2010-02-03 at 20:53 +0100, John Kacur wrote: > >> Balance local_irq_disable() and local_irq_enable() as well as > >> spin_lock_irq() and spin_lock_unlock_irq > >> > >> Signed-off-by: John Kacur > >> --- > >>  mm/vmscan.c |    3 ++- > >>  1 files changed, 2 insertions(+), 1 deletions(-) > >> > >> diff --git a/mm/vmscan.c b/mm/vmscan.c > >> index c26986c..b895025 100644 > >> --- a/mm/vmscan.c > >> +++ b/mm/vmscan.c > >> @@ -1200,8 +1200,9 @@ static unsigned long shrink_inactive_list(unsigned long max_scan, > >>               if (current_is_kswapd()) > >>                       __count_vm_events(KSWAPD_STEAL, nr_freed); > >>               __count_zone_vm_events(PGSTEAL, zone, nr_freed); > >> +             local_irq_enable(); > >> > >> -             spin_lock(&zone->lru_lock); > >> +             spin_lock_irq(&zone->lru_lock); > >>               /* > >>                * Put back any unfreeable pages. > >>                */ > > > > > > The above looks wrong. I don't know the code, but just by looking at > > where the locking and interrupts are, I can take a guess. > > > > Lets add a little more of the code: > > > >                local_irq_disable(); > >                if (current_is_kswapd()) > >                        __count_vm_events(KSWAPD_STEAL, nr_freed); > >                __count_zone_vm_events(PGSTEAL, zone, nr_freed); > > > >                spin_lock(&zone->lru_lock); > >                /* > > > > I'm guessing the __count_zone_vm_events and friends need interrupts > > disabled here, probably due to per cpu stuff. But if you enable > > interrupts before the spin_lock() you may let an interrupt come in and > > invalidate what was done above it. > > > > So no, I do not think enabling interrupts here is a good thing. > > > > okay, and since we have already done local_irq_disable(), then that is > why we only need the spin_lock() and not the spin_lock_irq() flavour? Yes, spin_lock_irq() is equivalent to spin_lock() + irq_disable(). Now, we already disabled irq. then, we only need spin_lock(). So, I don't think shrink_inactive_list need any fix.