From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 282BEC433C1 for ; Sat, 27 Mar 2021 03:35:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D639761A1E for ; Sat, 27 Mar 2021 03:35:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230258AbhC0Deg (ORCPT ); Fri, 26 Mar 2021 23:34:36 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:14495 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229880AbhC0DeQ (ORCPT ); Fri, 26 Mar 2021 23:34:16 -0400 Received: from DGGEMS403-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4F6kt401MkzySBp; Sat, 27 Mar 2021 11:32:12 +0800 (CST) Received: from [10.174.177.208] (10.174.177.208) by DGGEMS403-HUB.china.huawei.com (10.3.19.203) with Microsoft SMTP Server id 14.3.498.0; Sat, 27 Mar 2021 11:34:05 +0800 Subject: Re: [PATCH -next] mm, page_alloc: avoid page_to_pfn() in move_freepages() To: Matthew Wilcox References: <20210323131215.934472-1-liushixin2@huawei.com> <20210323125400.GE1719932@casper.infradead.org> CC: Andrew Morton , Stephen Rothwell , Michal Hocko , Vlastimil Babka , , , Kefeng Wang From: Liu Shixin Message-ID: Date: Sat, 27 Mar 2021 11:34:05 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20210323125400.GE1719932@casper.infradead.org> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.208] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry to reply to you after a so long time and thanks for your advice. It does seem that your proposed change will make the code cleaner and more efficient. I repeated move_freepages_block() 2000000 times on the VM and counted jiffies. The average value before and after the change was both about 12,000. I think it's probably because I'm using the Sparse Memory Model, so pfn_to_page() is not time-consuming. On 2021/3/23 20:54, Matthew Wilcox wrote: > On Tue, Mar 23, 2021 at 09:12:15PM +0800, Liu Shixin wrote: >> From: Kefeng Wang >> >> The start_pfn and end_pfn are already available in move_freepages_block(), >> there is no need to go back and forth between page and pfn in move_freepages >> and move_freepages_block, and pfn_valid_within() should validate pfn first >> before touching the page. > This looks good to me: > > Reviewed-by: Matthew Wilcox (Oracle) > >> static int move_freepages(struct zone *zone, >> - struct page *start_page, struct page *end_page, >> + unsigned long start_pfn, unsigned long end_pfn, >> int migratetype, int *num_movable) >> { >> struct page *page; >> + unsigned long pfn; >> unsigned int order; >> int pages_moved = 0; >> >> - for (page = start_page; page <= end_page;) { >> - if (!pfn_valid_within(page_to_pfn(page))) { >> - page++; >> + for (pfn = start_pfn; pfn <= end_pfn;) { >> + if (!pfn_valid_within(pfn)) { >> + pfn++; >> continue; >> } >> >> + page = pfn_to_page(pfn); > I wonder if this wouldn't be even better if we did: > > struct page *start_page = pfn_to_page(start_pfn); > > for (pfn = start_pfn; pfn <= end_pfn; pfn++) { > struct page *page = start_page + pfn - start_pfn; > > if (!pfn_valid_within(pfn)) > continue; > >> - >> - page++; >> + pfn++; >> continue; > ... then we can drop the increment of pfn here > >> } >> >> @@ -2458,7 +2459,7 @@ static int move_freepages(struct zone *zone, >> >> order = buddy_order(page); >> move_to_free_list(page, zone, order, migratetype); >> - page += 1 << order; >> + pfn += 1 << order; > ... and change this to pfn += (1 << order) - 1; > > Do you have any numbers to quantify the benefit of this change? > . >