Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935059Ab3DJV0K (ORCPT ); Wed, 10 Apr 2013 17:26:10 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:37460 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752182Ab3DJV0I (ORCPT ); Wed, 10 Apr 2013 17:26:08 -0400 Message-ID: <5165D8DE.5090801@linux.vnet.ibm.com> Date: Wed, 10 Apr 2013 14:25:50 -0700 From: Cody P Schafer User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Andrew Morton CC: Gilad Ben-Yossef , Simon Jeons , KOSAKI Motohiro , Mel Gorman , Linux MM , LKML Subject: Re: [PATCH v3 00/11] mm: fixup changers of per cpu pageset's ->high and ->batch References: <1365618219-17154-1-git-send-email-cody@linux.vnet.ibm.com> <20130410142354.6044338fd68ff2ad165b1bc8@linux-foundation.org> In-Reply-To: <20130410142354.6044338fd68ff2ad165b1bc8@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13041021-4834-0000-0000-000005A1E00E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1958 Lines: 39 On 04/10/2013 02:23 PM, Andrew Morton wrote: > On Wed, 10 Apr 2013 11:23:28 -0700 Cody P Schafer wrote: > >> "Problems" with the current code: >> 1. there is a lack of synchronization in setting ->high and ->batch in >> percpu_pagelist_fraction_sysctl_handler() >> 2. stop_machine() in zone_pcp_update() is unnecissary. >> 3. zone_pcp_update() does not consider the case where percpu_pagelist_fraction is non-zero >> >> To fix: >> 1. add memory barriers, a safe ->batch value, an update side mutex when >> updating ->high and ->batch, and use ACCESS_ONCE() for ->batch users that >> expect a stable value. >> 2. avoid draining pages in zone_pcp_update(), rely upon the memory barriers added to fix #1 >> 3. factor out quite a few functions, and then call the appropriate one. >> >> Note that it results in a change to the behavior of zone_pcp_update(), which is >> used by memory_hotplug. I'm rather certain 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. >> >> Further note that the draining of pages that previously took place in >> zone_pcp_update() occured after repeated draining when attempting to offline a >> page, and after the offline has "succeeded". It appears that the draining was >> added to zone_pcp_update() to avoid refactoring setup_pageset() into 2 >> funtions. > > There hasn't been a ton of review activity for this patchset :( > > I'm inclined to duck it until after 3.9. Do the patches fix any > noticeably bad userspace behavior? No, all the bugs are theoretical. Waiting should be fine. -- 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/