From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx152.postini.com [74.125.245.152]) by kanga.kvack.org (Postfix) with SMTP id A69B46B0032 for ; Thu, 15 Aug 2013 07:23:47 -0400 (EDT) Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 15 Aug 2013 21:13:31 +1000 Received: from d23relay03.au.ibm.com (d23relay03.au.ibm.com [9.190.235.21]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 9E4323578050 for ; Thu, 15 Aug 2013 21:23:42 +1000 (EST) Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay03.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7FBNOa47012842 for ; Thu, 15 Aug 2013 21:23:31 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r7FBNYdN008878 for ; Thu, 15 Aug 2013 21:23:34 +1000 Date: Thu, 15 Aug 2013 19:23:32 +0800 From: Wanpeng Li Subject: Re: [PATCH] mm: skip the page buddy block instead of one page Message-ID: <20130815112331.GA26134@hacker.(null)> Reply-To: Wanpeng Li References: <20130814163921.GC2706@gmail.com> <20130814180012.GO2296@suse.de> <520C3DD2.8010905@huawei.com> <20130815024427.GA2718@gmail.com> <520C4EFF.8040305@huawei.com> <20130815041736.GA2592@gmail.com> <20130815042434.GA3139@gmail.com> <520C8707.4000100@huawei.com> <20130815095102.GA4449@hacker.(null)> <520CB84D.6000306@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <520CB84D.6000306@huawei.com> Sender: owner-linux-mm@kvack.org List-ID: To: Xishi Qiu Cc: Minchan Kim , Mel Gorman , Andrew Morton , riel@redhat.com, aquini@redhat.com, linux-mm@kvack.org, LKML On Thu, Aug 15, 2013 at 07:15:25PM +0800, Xishi Qiu wrote: >On 2013/8/15 17:51, Wanpeng Li wrote: > >> On Thu, Aug 15, 2013 at 03:45:11PM +0800, Xishi Qiu wrote: >>> On 2013/8/15 12:24, Minchan Kim wrote: >>> >>>>> Please read full thread in detail. >>>>> >>>>> Mel suggested following as >>>>> >>>>> if (PageBuddy(page)) { >>>>> int nr_pages = (1 << page_order(page)) - 1; >>>>> if (PageBuddy(page)) { >>>>> nr_pages = min(nr_pages, MAX_ORDER_NR_PAGES - 1); >>>>> low_pfn += nr_pages; >>>>> continue; >>>>> } >>>>> } >>>>> >>>>> min(nr_pages, xxx) removes your concern but I think Mel's version >>>>> isn't right. It should be aligned with pageblock boundary so I >>>>> suggested following. >>>>> >>>>> if (PageBuddy(page)) { >>>>> #ifdef CONFIG_MEMORY_ISOLATION >>>>> unsigned long order = page_order(page); >>>>> if (PageBuddy(page)) { >>>>> low_pfn += (1 << order) - 1; >>>>> low_pfn = min(low_pfn, end_pfn); >>>>> } >>>>> #endif >>>>> continue; >>>>> } >>>>> >>> >>> Hi Minchan, >>> >>> I understand now, but why use "end_pfn" here? >>> Maybe like this: >>> >>> if (PageBuddy(page)) { >>> /* >>> * page_order is racy without zone->lock but worst case >>> * by the racing is just skipping pageblock_nr_pages. >>> */ >>> unsigned long nr_pages = 1 << page_order(page); >>> if (likely(PageBuddy(page))) { >>> nr_pages = min(nr_pages, MAX_ORDER_NR_PAGES); >> >> How much sense it make? nr_pages is still equal to itself since nr_pages can't >> larger than MAX_ORDER_NR_PAGES. >> > >Hi Wanpeng, > >Mel pointed "page_order cannot be used unless zone->lock is held". >"Even if the page is still page buddy, there is no guarantee that it's >the same page order as the first read. It could have be currently merging >with adjacent buddies for example." > >If someone use the page during the double PageBuddy check, the value >of private may be wrong. In my opinion, just keep the code unchanged. > Hi Xishi, You miss my point, I mean nr_pages = min(nr_pages, MAX_ORDER_NR_PAGES); not make sense since nr_pages can't larger then MAX_ORDER_NR_PAGES. Regards, Wanpeng Li >Thanks, >Xishi Qiu > >>> >>> /* Align with pageblock boundary */ >>> if ((low_pfn & (pageblock_nr_pages - 1)) + nr_pages > >>> pageblock_nr_pages) >>> low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1; >>> else >>> low_pfn += nr_pages - 1; >>> } >>> continue; >>> } >>> >>> Thanks, >>> Xishi Qiu >>> >>>>> so worst case is (pageblock_nr_pages - 1). >>>>> but we don't need to add CONFIG_MEMORY_ISOLATION so my suggestion >>>>> is following as. >>>>> >>>>> if (PageBuddy(page)) { >>>>> unsigned long order = page_order(page); >>>>> if (PageBuddy(page)) { >>>>> low_pfn += (1 << order) - 1; >>>>> low_pfn = min(low_pfn, end_pfn); >>>> >>>> Maybe it should be low_pfn = min(low_pfn, end_pfn - 1). >>>> >>>> >>>>> } >>>>> continue; >>>>> } >>>>> > > -- 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