Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935536Ab3DHWSv (ORCPT ); Mon, 8 Apr 2013 18:18:51 -0400 Received: from mail-qc0-f177.google.com ([209.85.216.177]:35668 "EHLO mail-qc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934642Ab3DHWSu (ORCPT ); Mon, 8 Apr 2013 18:18:50 -0400 Message-ID: <5163424A.4000106@gmail.com> Date: Mon, 08 Apr 2013 18:18:50 -0400 From: KOSAKI Motohiro User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130307 Thunderbird/17.0.4 MIME-Version: 1.0 To: Cody P Schafer CC: KOSAKI Motohiro , Andrew Morton , Mel Gorman , Linux MM , LKML Subject: Re: [PATCH 2/3] mm/page_alloc: convert zone_pcp_update() to use on_each_cpu() instead of stop_machine() References: <1365194030-28939-1-git-send-email-cody@linux.vnet.ibm.com> <1365194030-28939-3-git-send-email-cody@linux.vnet.ibm.com> <5161931A.8060501@gmail.com> <5162FF18.8010802@linux.vnet.ibm.com> <516319FF.6030104@gmail.com> <51631F4D.7050504@linux.vnet.ibm.com> In-Reply-To: <51631F4D.7050504@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2839 Lines: 73 (4/8/13 3:49 PM), Cody P Schafer wrote: > On 04/08/2013 12:26 PM, KOSAKI Motohiro wrote: >> (4/8/13 1:32 PM), Cody P Schafer wrote: >>> On 04/07/2013 08:39 AM, KOSAKI Motohiro wrote: >>>> (4/5/13 4:33 PM), Cody P Schafer wrote: >>>>> No off-cpu users of the percpu pagesets exist. >>>>> >>>>> zone_pcp_update()'s goal is to adjust the ->high and ->mark members of a >>>>> percpu pageset based on a zone's ->managed_pages. We don't need to drain >>>>> the entire percpu pageset just to modify these fields. Avoid calling >>>>> setup_pageset() (and the draining required to call it) and instead just >>>>> set the fields' values. >>>>> >>>>> This does change the behavior of zone_pcp_update() as the percpu >>>>> pagesets will not be drained when zone_pcp_update() is called (they will >>>>> end up being shrunk, not completely drained, later when a 0-order page >>>>> is freed in free_hot_cold_page()). >>>>> >>>>> Signed-off-by: Cody P Schafer >>>> >>>> NAK. >>>> >>>> 1) zone_pcp_update() is only used from memory hotplug and it require page drain. >>> >>> I'm looking at this code because I'm currently working on a patchset >>> which adds another interface which modifies zone sizes, so "only used >>> from memory hotplug" is a temporary thing (unless I discover that >>> zone_pcp_update() is not intended to do what I want it to do). >> >> maybe yes, maybe no. I don't know temporary or not. However the fact is, >> you must not break anywhere. You need to look all caller always. > > Right, which is why I want to understand memory hotplug's actual > requirements. > >>>> 2) stop_machin is used for avoiding race. just removing it is insane. >>> >>> What race? Is there a cross cpu access to ->high & ->batch that makes >>> using on_each_cpu() instead of stop_machine() inappropriate? It is >>> absolutely not just being removed. >> >> OK, I missed that. however your code is still wrong. >> However you can't call free_pcppages_bulk() from interrupt context and >> then you can't use on_each_cpu() anyway. > > Given drain_pages() implementation, I find that hard to believe (It uses > on_each_cpu_mask() and eventually calls free_pcppages_bulk()). > > Can you provide a reference backing up your statement? Grr. I missed again. OK you are right. go ahead. > If this turns out to be an issue, schedule_on_each_cpu() could be an > alternative. no way. schedule_on_each_cpu() is more problematic and it should be removed in the future. schedule_on_each_cpu() can only be used when caller task don't have any lock. otherwise it may make deadlock. -- 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/