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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 31C35C636C9 for ; Sat, 17 Jul 2021 18:41:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D5056115C for ; Sat, 17 Jul 2021 18:41:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235010AbhGQSoZ (ORCPT ); Sat, 17 Jul 2021 14:44:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48402 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234625AbhGQSoY (ORCPT ); Sat, 17 Jul 2021 14:44:24 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1D920C061762; Sat, 17 Jul 2021 11:41:27 -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:To:From:Date:Sender:Reply-To:Cc: Content-Transfer-Encoding:Content-ID:Content-Description; bh=34IDPVr1FFgLa52/AyVJqWmL3gtZnKkbcxspv1mGiNc=; b=I2b1oobDIa9kR66Da+BrMpc96u 8qwvH+/Bzx9JFf2cZXlzgwO7lopBcV9cvwWLWo4tPAqfskgTbVnSxk969GtFfdRsVJ10jxWvYMeJr /AhW3bBHX7rLl2SYQUpz0r+F2Rk1fLECQDEM2pNTGB1k71nHkvq+/5vOcAcHox4oWj7R2EJ59nW5u SfA5gk4IUeM+gdGAjSZQoqs0v59/FTotmz5e+1zjNzsJ6pUhe/mR7E4Cuyw0uRPs8yW08QM3JFwzx L4HRbGanuBnmEvb6furh2pwZJKqeKHmLMJ07Y+ZsF8rdre0OKZfyVYjzs8h/nGf2qgrJ0plAsOT/0 Djc9zL5A==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m4pEv-005Tso-4z; Sat, 17 Jul 2021 18:40:49 +0000 Date: Sat, 17 Jul 2021 19:40:41 +0100 From: Matthew Wilcox To: Andreas =?iso-8859-1?Q?Gr=FCnbacher?= , Christoph Hellwig , linux-erofs@lists.ozlabs.org, Linux FS-devel Mailing List , LKML , "Darrick J. Wong" , Chao Yu , Liu Bo , Joseph Qi , Liu Jiang Subject: Re: [PATCH 1/2] iomap: support tail packing inline read Message-ID: References: <20210716050724.225041-1-hsiangkao@linux.alibaba.com> <20210716050724.225041-2-hsiangkao@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jul 17, 2021 at 11:15:58PM +0800, Gao Xiang wrote: > Hi Matthew, > > On Sat, Jul 17, 2021 at 04:01:38PM +0100, Matthew Wilcox wrote: > > On Sat, Jul 17, 2021 at 09:38:18PM +0800, Gao Xiang wrote: > > > Sorry about some late. I've revised a version based on Christoph's > > > version and Matthew's thought above. I've preliminary checked with > > > EROFS, if it does make sense, please kindly help check on the gfs2 > > > side as well.. > > > > I don't understand how this bit works: > > This part inherited from the Christoph version without change. > The following thoughts are just my own understanding... > > > > > > struct page *page = ctx->cur_page; > > > - struct iomap_page *iop; > > > + struct iomap_page *iop = NULL; > > > bool same_page = false, is_contig = false; > > > loff_t orig_pos = pos; > > > unsigned poff, plen; > > > sector_t sector; > > > > > > - if (iomap->type == IOMAP_INLINE) { > > > - WARN_ON_ONCE(pos); > > > - iomap_read_inline_data(inode, page, iomap); > > > - return PAGE_SIZE; > > > - } > > > + if (iomap->type == IOMAP_INLINE && !pos) > > > + WARN_ON_ONCE(to_iomap_page(page) != NULL); > > > + else > > > + iop = iomap_page_create(inode, page); > > > > Imagine you have a file with bytes 0-2047 in an extent which is !INLINE > > and bytes 2048-2051 in the INLINE extent. When you read the page, first > > you create an iop for the !INLINE extent. Then this function is called > > Yes, it first created an iop for the !INLINE extent. > > > again for the INLINE extent and you'll hit the WARN_ON_ONCE. No? > > If it is called again with another INLINE extent, pos will be non-0? > so (!pos) == false. Am I missing something? Well, either sense of a WARN_ON is wrong. For a file which is PAGE_SIZE + 3 bytes in size, to_iomap_page() will be NULL. For a file which is PAGE_SIZE/2 + 3 bytes in size, to_iomap_page() will not be NULL. (assuming the block size is <= PAGE_SIZE / 2). I think we need a prep patch that looks something like this: +++ b/fs/iomap/buffered-io.c @@ -252,8 +252,12 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data, return PAGE_SIZE; } + if (offset_in_page(pos) || length < PAGE_SIZE) + iop = iomap_page_create(inode, page); + else + iop = NULL; + /* zero post-eof blocks as the page may be mapped */ - iop = iomap_page_create(inode, page); iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen); if (plen == 0) goto done; ie first get the conditions right under which we should create an iop.