From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx201.postini.com [74.125.245.201]) by kanga.kvack.org (Postfix) with SMTP id A7AB96B0027 for ; Tue, 9 Apr 2013 02:06:18 -0400 (EDT) Received: by mail-la0-f47.google.com with SMTP id fj20so6122145lab.34 for ; Mon, 08 Apr 2013 23:06:16 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1365194030-28939-1-git-send-email-cody@linux.vnet.ibm.com> <1365194030-28939-4-git-send-email-cody@linux.vnet.ibm.com> <5162FE4D.7020308@linux.vnet.ibm.com> Date: Tue, 9 Apr 2013 09:06:16 +0300 Message-ID: Subject: Re: [PATCH 3/3] mm: when handling percpu_pagelist_fraction, use on_each_cpu() to set percpu pageset fields. From: Gilad Ben-Yossef Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Cody P Schafer Cc: Andrew Morton , Mel Gorman , Linux MM , LKML On Tue, Apr 9, 2013 at 9:03 AM, Gilad Ben-Yossef wrote: > >> I also wonder whether there could be unexpected interactions between ->high >> and ->batch not changing together atomically. For example, could adjusting >> this knob cause ->batch to rise enough that it is greater than the previous >> ->high? If the code above then runs with the previous ->high, ->count >> wouldn't be correct (checking this inside free_pcppages_bulk() might help on >> this one issue). > > You are right, but that can be treated in setup_pagelist_highmark() e.g.: > > 3993 static void setup_pagelist_highmark(struct per_cpu_pageset *p, > 3994 unsigned long high) > 3995 { > 3996 struct per_cpu_pages *pcp; > unsigned int batch; > 3997 > 3998 pcp = &p->pcp; > /* We're about to mess with PCP in an non atomic fashion. > Put an intermediate safe value of batch and make sure it > is visible before any other change */ > pcp->batch = 1UL; > smb_mb(); > > 3999 pcp->high = high; and i think I missed another needed barrier here: smp_mb(); > > 4000 batch = max(1UL, high/4); > 4001 if ((high/4) > (PAGE_SHIFT * 8)) > 4002 batch = PAGE_SHIFT * 8; > > pcp->batch = batch; > 4003 } > -- Gilad Ben-Yossef Chief Coffee Drinker gilad@benyossef.com Israel Cell: +972-52-8260388 US Cell: +1-973-8260388 http://benyossef.com "If you take a class in large-scale robotics, can you end up in a situation where the homework eats your dog?" -- Jean-Baptiste Queru -- 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