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 3ED43C49EA7 for ; Mon, 28 Jun 2021 06:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1A94661945 for ; Mon, 28 Jun 2021 06:29:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232069AbhF1Gb0 (ORCPT ); Mon, 28 Jun 2021 02:31:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229911AbhF1Gb0 (ORCPT ); Mon, 28 Jun 2021 02:31:26 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F04D9C061574; Sun, 27 Jun 2021 23:29:00 -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=8cTi4WGWVG2C120IO8WXCGutLnZwDIpaPEZ82wXkV+I=; b=tfarKpP8v6HFfCRc4oPK53+lEp kAsNYstY133Xrj6wY+iRY2blwaUJNgk1aeZGikyqy9k6tg/JrwaaW5S0E5eGwJX6pqWu+wTJo/KR+ xt9heM8cLmFbCUxe6AVpkt4yY1ZJza+qpBvX6EJlyVilaUH5SgB15TFcdl9fPxYB4/O6b3sXoDvNJ AZdka/FRVm3jSrj+MI0YAggREVpK12ImlYWtmpTR6LMgOwmXDNOCHPfa0pnk2qXq2xL3cBZp4yFWh FR65y632uMUcBxZBy3u9vQkn9uuThGDR51z1zkw/8A1PGnfYp5EodsXI4dmx2NAQzg25/DrXVeUPg O6Bpbvbw==; Received: from hch by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lxkjR-002ep3-Cr; Mon, 28 Jun 2021 06:27:13 +0000 Date: Mon, 28 Jun 2021 07:26:57 +0100 From: Christoph Hellwig To: Matthew Wilcox Cc: Christoph Hellwig , 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: 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 On Thu, Jun 24, 2021 at 07:02:23PM +0100, Matthew Wilcox wrote: > > What is the advantage of copying backwards here to start with? > > Easier to write the loop this way? I suppose we could do it as ... > > unsigned int i, nr = folio_nr_pages(folio); > > for (i = 0; i < nr; i++) { > /* folio_page() handles discontinuities in memmap */ > copy_highpage(folio_page(newfolio, i), folio_page(folio, i)); > cond_resched(); > } I'd prefer that if there is no obvious downside.