Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935656Ab3DHT07 (ORCPT ); Mon, 8 Apr 2013 15:26:59 -0400 Received: from mail-qc0-f179.google.com ([209.85.216.179]:41797 "EHLO mail-qc0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762074Ab3DHT05 (ORCPT ); Mon, 8 Apr 2013 15:26:57 -0400 Message-ID: <516319FF.6030104@gmail.com> Date: Mon, 08 Apr 2013 15:26:55 -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> In-Reply-To: <5162FF18.8010802@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2036 Lines: 51 (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. >> 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. -- 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/