From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx171.postini.com [74.125.245.171]) by kanga.kvack.org (Postfix) with SMTP id 0867C6B0006 for ; Mon, 8 Apr 2013 15:49:44 -0400 (EDT) Received: from /spool/local by e7.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 8 Apr 2013 15:49:43 -0400 Received: from d01relay03.pok.ibm.com (d01relay03.pok.ibm.com [9.56.227.235]) by d01dlp03.pok.ibm.com (Postfix) with ESMTP id D7EBAC9001E for ; Mon, 8 Apr 2013 15:49:41 -0400 (EDT) Received: from d01av05.pok.ibm.com (d01av05.pok.ibm.com [9.56.224.195]) by d01relay03.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r38JnfP1264284 for ; Mon, 8 Apr 2013 15:49:41 -0400 Received: from d01av05.pok.ibm.com (loopback [127.0.0.1]) by d01av05.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r38Jnfdi020782 for ; Mon, 8 Apr 2013 15:49:41 -0400 Message-ID: <51631F4D.7050504@linux.vnet.ibm.com> Date: Mon, 08 Apr 2013 12:49:33 -0700 From: Cody P Schafer MIME-Version: 1.0 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> In-Reply-To: <516319FF.6030104@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: KOSAKI Motohiro Cc: Andrew Morton , Mel Gorman , Linux MM , LKML 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? If this turns out to be an issue, schedule_on_each_cpu() could be an alternative. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org