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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 E9105C48BC2 for ; Wed, 23 Jun 2021 08:37:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC72D61164 for ; Wed, 23 Jun 2021 08:37:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229978AbhFWIkJ (ORCPT ); Wed, 23 Jun 2021 04:40:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229833AbhFWIkG (ORCPT ); Wed, 23 Jun 2021 04:40:06 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D7116C061574; Wed, 23 Jun 2021 01:37:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rM2Yp+8Itjz90D0EXjNMSXvd4FeigAopuxmvxgM0gQY=; b=XlkpC2A5OOR2l6x79e+08Mm8OT 9tWohCTbGn4GV+5+sIvTjLkW8POgOoFdW5IK/lqJtgwDwPIsSRxGOIY6o1PiSyvoofnuk1u7tW9+K Ez34DmiuekyOaZ6e0Jd2R2YaegIPowfIwl4ST+E5rnAvzNXhdVPwQvazgcd8mgXdbN9LESJCNsspE 7Jp+3FlpR0KlX13Bv/0ft0WRSxj9JH0+RqpBoBxiqEInsMqPa6jd54wwNL4+4ZZEamlNtopDB92bH sgXS2vhn/7VrQcR4ElYLIBuddMHHOJ8Iv6waBHNmUrNleouDtNmEMrSoDrd1jVooxwrOKHgJv4CyL DNyDJ+lg==; Received: from 089144193030.atnat0002.highway.a1.net ([89.144.193.30] helo=localhost) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvyNj-00FDev-Gr; Wed, 23 Jun 2021 08:37:18 +0000 Date: Wed, 23 Jun 2021 10:35:00 +0200 From: Christoph Hellwig To: "Matthew Wilcox (Oracle)" Cc: akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 20/46] mm/migrate: Add folio_migrate_copy() Message-ID: References: <20210622121551.3398730-1-willy@infradead.org> <20210622121551.3398730-21-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210622121551.3398730-21-willy@infradead.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > +void folio_migrate_copy(struct folio *newfolio, struct folio *folio) > { > + unsigned int i = folio_nr_pages(folio) - 1; > > + copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); > + while (i-- > 0) { > + cond_resched()a > + /* folio_page() handles discontinuities in memmap */ > + copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); > + } > + What is the advantage of copying backwards here to start with?