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=ham 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 43B3CC433C1 for ; Sat, 27 Mar 2021 03:34:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 95DB561A1E for ; Sat, 27 Mar 2021 03:34:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 95DB561A1E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B5AE76B006C; Fri, 26 Mar 2021 23:34:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id AE4246B006E; Fri, 26 Mar 2021 23:34:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 95EB16B0070; Fri, 26 Mar 2021 23:34:20 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0198.hostedemail.com [216.40.44.198]) by kanga.kvack.org (Postfix) with ESMTP id 79E476B006C for ; Fri, 26 Mar 2021 23:34:20 -0400 (EDT) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 30513180AD5DA for ; Sat, 27 Mar 2021 03:34:20 +0000 (UTC) X-FDA: 77964236280.17.451A118 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) by imf16.hostedemail.com (Postfix) with ESMTP id BB0BB80192CE for ; Sat, 27 Mar 2021 03:34:17 +0000 (UTC) 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 X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BB0BB80192CE X-Stat-Signature: qasemad6rnie6qbebxc3qyk54875os9j Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf16; identity=mailfrom; envelope-from=""; helo=szxga05-in.huawei.com; client-ip=45.249.212.191 X-HE-DKIM-Result: none/none X-HE-Tag: 1616816057-401184 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? > . >