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=-0.6 required=3.0 tests=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 03BA3C11D0F for ; Thu, 20 Feb 2020 16:24:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C6631206F4 for ; Thu, 20 Feb 2020 16:24:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="lxTIdidZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728377AbgBTQYF (ORCPT ); Thu, 20 Feb 2020 11:24:05 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:35548 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727709AbgBTQYF (ORCPT ); Thu, 20 Feb 2020 11:24:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=/X+cuahXNVjwX8kIjzPU/QZUMEm+qIm+lNxfvhlX3EA=; b=lxTIdidZw2P2UO9t/Oji3FNceT +CjnxJZogq66GLHl3rhRoufVhXPoH7CxN5rw1pgrMvr7szk03lJeq2TvDL3R2ys6m86hnGj7sXBXg AQaHFo4WLWH90RnuR6backVMmU/lhsJTXMH7V42hfdxcXElLYWAoi8WkszieVn0N2xZmXUiT1EECe GJX8uJUjnaFLb7zI2vKxvhhrKwSedVafnnaMtZd9zrJbg6npgPtnxSYDtx+h9J81ITalXizKXonPp SQVVA+pyipbUonuljCpyE7+n90vEPRYltjJb/REqxUNVBonREpCV+ttQEEWV7EF1CEorahGhIHM1b 9p1J3F8g==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4ocO-0001zg-A1; Thu, 20 Feb 2020 16:24:04 +0000 Date: Thu, 20 Feb 2020 08:24:04 -0800 From: Matthew Wilcox To: Christoph Hellwig Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-erofs@lists.ozlabs.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, ocfs2-devel@oss.oracle.com, linux-xfs@vger.kernel.org Subject: Re: [PATCH v7 21/24] iomap: Restructure iomap_readpages_actor Message-ID: <20200220162404.GY24185@bombadil.infradead.org> References: <20200219210103.32400-1-willy@infradead.org> <20200219210103.32400-22-willy@infradead.org> <20200220154741.GB19577@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200220154741.GB19577@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Feb 20, 2020 at 07:47:41AM -0800, Christoph Hellwig wrote: > On Wed, Feb 19, 2020 at 01:01:00PM -0800, Matthew Wilcox wrote: > > From: "Matthew Wilcox (Oracle)" > > > > By putting the 'have we reached the end of the page' condition at the end > > of the loop instead of the beginning, we can remove the 'submit the last > > page' code from iomap_readpages(). Also check that iomap_readpage_actor() > > didn't return 0, which would lead to an endless loop. > > I'm obviously biassed a I wrote the original code, but I find the new > very much harder to understand (not that the previous one was easy, this > is tricky code..). Agreed, I found the original code hard to understand. I think this is easier because now cur_page doesn't leak outside this loop, so it has an obvious lifecycle. I'm kind of optimistic for Dave Howells' iov_iter addition of an ITER_MAPPING. That might simplify all of this code.