Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936447Ab3DJVX5 (ORCPT ); Wed, 10 Apr 2013 17:23:57 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:55533 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934746Ab3DJVXz (ORCPT ); Wed, 10 Apr 2013 17:23:55 -0400 Date: Wed, 10 Apr 2013 14:23:54 -0700 From: Andrew Morton To: Cody P Schafer 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 Message-Id: <20130410142354.6044338fd68ff2ad165b1bc8@linux-foundation.org> In-Reply-To: <1365618219-17154-1-git-send-email-cody@linux.vnet.ibm.com> References: <1365618219-17154-1-git-send-email-cody@linux.vnet.ibm.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1814 Lines: 36 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? -- 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/