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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 19CADC49EA6 for ; Thu, 24 Jun 2021 18:02:48 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B60AD613EE for ; Thu, 24 Jun 2021 18:02:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B60AD613EE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A8A9A6B0036; Thu, 24 Jun 2021 14:02:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A39876B005D; Thu, 24 Jun 2021 14:02:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 901066B006C; Thu, 24 Jun 2021 14:02:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0174.hostedemail.com [216.40.44.174]) by kanga.kvack.org (Postfix) with ESMTP id 532AD6B0036 for ; Thu, 24 Jun 2021 14:02:46 -0400 (EDT) Received: from smtpin36.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 69CBD182371AA for ; Thu, 24 Jun 2021 18:02:46 +0000 (UTC) X-FDA: 78289387932.36.488400C Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf19.hostedemail.com (Postfix) with ESMTP id 06E5F9001E5E for ; Thu, 24 Jun 2021 18:02:45 +0000 (UTC) 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=hLMjV/v2VMW7OPL88d4Rhvuc3mEsgbM4ADked1xlhzM=; b=OHOaogABad5RWlFl/ORqOrRUMA 6yixELjA4e+dg38K3YPau19P+odwDhSWSG+qmbCPbwYiRZ3HIhAZQ5X03bQDB1SwYpuHCixP6ORDz KjT0AoFb4c3AF29QUH8h1rkjqTo8JIT8cA7Oh+xIRDxp9tPJiwkmJ+/FT8dea8X5pURKDHWFotm1R G1RnJKz6e4505XgtMZP+oGax3wRNI9x/xKE9EB+JIkCg1qveEVTabu3d67pZaEcDz9LWNsqEafOR6 y+f9RoW1k1regH8wqMs4WXj0jrtC35rr/h3QutwKT09E7j1EwX/U+ya407u56/cDvERSQKYeG014N /ixOAgNg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1lwTgF-00GqhW-Dz; Thu, 24 Jun 2021 18:02:25 +0000 Date: Thu, 24 Jun 2021 19:02:23 +0100 From: Matthew Wilcox To: Christoph Hellwig 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: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 06E5F9001E5E Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=OHOaogAB; spf=none (imf19.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Stat-Signature: p1atuzr4fqi5m9sb7c7j4wqu535kj59f X-HE-Tag: 1624557765-306069 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: On Wed, Jun 23, 2021 at 10:35:00AM +0200, Christoph Hellwig wrote: > > +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? 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'm not really bothered. As long as we don't call folio_nr_pages() for each iteration of the loop ... I've actually been wondering about marking that as __pure, but I don't quite have the nerve to do it yet.