From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752880Ab2AASwg (ORCPT ); Sun, 1 Jan 2012 13:52:36 -0500 Received: from mail-ee0-f46.google.com ([74.125.83.46]:38421 "EHLO mail-ee0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751124Ab2AASwd convert rfc822-to-8bit (ORCPT ); Sun, 1 Jan 2012 13:52:33 -0500 Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes To: "Gilad Ben-Yossef" Cc: "Marek Szyprowski" , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, linux-mm@kvack.org, linaro-mm-sig@lists.linaro.org, "Kyungmin Park" , "Russell King" , "Andrew Morton" , "KAMEZAWA Hiroyuki" , "Daniel Walker" , "Mel Gorman" , "Arnd Bergmann" , "Jesse Barker" , "Jonathan Corbet" , "Shariq Hasnain" , "Chunsang Jeong" , "Dave Hansen" , "Benjamin Gaignard" Subject: Re: [PATCH 01/11] mm: page_alloc: set_migratetype_isolate: drain PCP prior to isolating References: <1325162352-24709-1-git-send-email-m.szyprowski@samsung.com> <1325162352-24709-2-git-send-email-m.szyprowski@samsung.com> Date: Sun, 01 Jan 2012 19:52:16 +0100 MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT From: "Michal Nazarewicz" Message-ID: In-Reply-To: User-Agent: Opera Mail/11.60 (Linux) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 01 Jan 2012 17:06:53 +0100, Gilad Ben-Yossef wrote: > 2012/1/1 Michal Nazarewicz : >> Looks interesting, I'm not entirely sure why it does not end up a race >> condition, but in case of __zone_drain_all_pages() we already hold > If a page is in the PCP list when we check, you'll send the IPI and all is well. > > If it isn't when we check and gets added later you could just the same have > situation where we send the IPI, try to do try an empty PCP list and then > the page gets added. So we are not adding a race condition that is not there > already :-) Right, makes sense. >> zone->lock, so my fears are somehow gone.. I'll give it a try, and prepare >> a patch for __zone_drain_all_pages(). > I plan to send V5 of the IPI noise patch after some testing. It has a new > version of the drain_all_pages, with no allocation in the reclaim path > and no locking. You might want to wait till that one is out to base on it. This shouldn't be a problem for my case as set_migratetype_isolate() is hardly ever called in reclaim path. :) The change so far seems rather obvious: mm/page_alloc.c | 14 +++++++++++++- 1 files changed, 13 insertions(+), 1 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 424d36a..eaa686b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1181,7 +1181,19 @@ static void __zone_drain_local_pages(void *arg) */ static void __zone_drain_all_pages(struct zone *zone) { - on_each_cpu(__zone_drain_local_pages, zone, 1); + struct per_cpu_pageset *pcp; + cpumask_var_t cpus; + int cpu; + + if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC | __GFP_NOWARN))) { + for_each_online_cpu(cpu) + if (per_cpu_ptr(zone->pageset, cpu)->pcp.count) + cpumask_set_cpu(cpu, cpus); + on_each_cpu_mask(cpus, __zone_drain_local_pages, zone, 1); + free_cpumask_var(cpus); + } else { + on_each_cpu(__zone_drain_local_pages, zone, 1); + } } #ifdef CONFIG_HIBERNATION -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Michał “mina86” Nazarewicz (o o) ooo +------------------ooO--(_)--Ooo--