From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx136.postini.com [74.125.245.136]) by kanga.kvack.org (Postfix) with SMTP id BA0726B0037 for ; Mon, 8 Apr 2013 15:08:12 -0400 (EDT) Received: by mail-qe0-f52.google.com with SMTP id jy17so3246308qeb.25 for ; Mon, 08 Apr 2013 12:08:11 -0700 (PDT) Message-ID: <5163159A.20800@gmail.com> Date: Mon, 08 Apr 2013 15:08:10 -0400 From: KOSAKI Motohiro MIME-Version: 1.0 Subject: Re: [PATCH 0/3] mm: fixup changers of per cpu pageset's ->high and ->batch References: <1365194030-28939-1-git-send-email-cody@linux.vnet.ibm.com> <51618F5A.3060005@gmail.com> <5162FB82.5020607@linux.vnet.ibm.com> In-Reply-To: <5162FB82.5020607@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-2022-JP Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Cody P Schafer Cc: KOSAKI Motohiro , Andrew Morton , Mel Gorman , Linux MM , LKML (4/8/13 1:16 PM), Cody P Schafer wrote: > On 04/07/2013 08:23 AM, KOSAKI Motohiro wrote: >> (4/5/13 4:33 PM), Cody P Schafer wrote: >>> In one case while modifying the ->high and ->batch fields of per cpu pagesets >>> we're unneededly using stop_machine() (patches 1 & 2), and in another we don't have any >>> syncronization at all (patch 3). >>> >>> This patchset fixes both of them. >>> >>> Note that it results in a change to the behavior of zone_pcp_update(), which is >>> used by memory_hotplug. I _think_ that I've diserned (and preserved) the >>> essential behavior (changing ->high and ->batch), and only eliminated unneeded >>> actions (draining the per cpu pages), but this may not be the case. >> >> at least, memory hotplug need to drain. > > Could you explain why the drain is required here? From what I can tell, > after the stop_machine() completes, the per cpu page sets could be > repopulated at any point, making the combination of draining and > modifying ->batch & ->high uneeded. Then, memory hotplug again and again try to drain. Moreover hotplug prevent repopulation by using MIGRATE_ISOLATE. pcp never be page count == 0 and it prevent memory hot remove. -- 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