From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932136Ab2IDJ4J (ORCPT ); Tue, 4 Sep 2012 05:56:09 -0400 Received: from fgwmail6.fujitsu.co.jp ([192.51.44.36]:34838 "EHLO fgwmail6.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756736Ab2IDJzb (ORCPT ); Tue, 4 Sep 2012 05:55:31 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.7.4 Message-ID: <5045CFD6.9040408@jp.fujitsu.com> Date: Tue, 4 Sep 2012 18:54:30 +0900 From: Yasuaki Ishimatsu User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:15.0) Gecko/20120824 Thunderbird/15.0 MIME-Version: 1.0 To: Wen Congyang CC: Andrew Morton , , , , , , , , , , , , , , , , , , Subject: Re: [RFC v8 PATCH 13/20] memory-hotplug: check page type in get_page_bootmem References: <1346148027-24468-1-git-send-email-wency@cn.fujitsu.com> <1346148027-24468-14-git-send-email-wency@cn.fujitsu.com> <20120831143032.1343e99a.akpm@linux-foundation.org> <50457983.1050304@cn.fujitsu.com> In-Reply-To: <50457983.1050304@cn.fujitsu.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Wen, 2012/09/04 12:46, Wen Congyang wrote: > Hi, isimatu-san > > At 09/01/2012 05:30 AM, Andrew Morton Wrote: >> On Tue, 28 Aug 2012 18:00:20 +0800 >> wency@cn.fujitsu.com wrote: >> >>> From: Yasuaki Ishimatsu >>> >>> There is a possibility that get_page_bootmem() is called to the same page many >>> times. So when get_page_bootmem is called to the same page, the function only >>> increments page->_count. >> >> I really don't understand this explanation, even after having looked at >> the code. Can you please have another attempt at the changelog? > > What is the problem that you want to fix? The function get_page_bootmem() > may be called to the same page more than once, but I don't find any problem > about current implementation. The patch is just optimization. The patch does not fix a problems. As you know, the function may be called many times for the same page. I think if a page is sets to page_type and Page Private flag and page->private, the page need not be set the same things again. So we check page_type when get_page_bootmem() is called. And if the page has been set to them, the page is only incremented page->_count. Thanks, Yasuaki Ishimatsu > > Thanks > Wen Congyang > >> >>> --- a/mm/memory_hotplug.c >>> +++ b/mm/memory_hotplug.c >>> @@ -95,10 +95,17 @@ static void release_memory_resource(struct resource *res) >>> static void get_page_bootmem(unsigned long info, struct page *page, >>> unsigned long type) >>> { >>> - page->lru.next = (struct list_head *) type; >>> - SetPagePrivate(page); >>> - set_page_private(page, info); >>> - atomic_inc(&page->_count); >>> + unsigned long page_type; >>> + >>> + page_type = (unsigned long) page->lru.next; >>> + if (page_type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE || >>> + page_type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE){ >>> + page->lru.next = (struct list_head *) type; >>> + SetPagePrivate(page); >>> + set_page_private(page, info); >>> + atomic_inc(&page->_count); >>> + } else >>> + atomic_inc(&page->_count); >>> } >> >> And a code comment which explains what is going on would be good. As >> is always the case ;) >> >> >