From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx102.postini.com [74.125.245.102]) by kanga.kvack.org (Postfix) with SMTP id 133E96B0006 for ; Wed, 10 Apr 2013 17:23:55 -0400 (EDT) Date: Wed, 10 Apr 2013 14:23:54 -0700 From: Andrew Morton 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Cody P Schafer Cc: Gilad Ben-Yossef , Simon Jeons , KOSAKI Motohiro , Mel Gorman , Linux MM , LKML 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, 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