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 7B091C34047 for ; Wed, 19 Feb 2020 17:06:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 53BB524676 for ; Wed, 19 Feb 2020 17:06:46 +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="YD6KASfC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726927AbgBSRGp (ORCPT ); Wed, 19 Feb 2020 12:06:45 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:37054 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726558AbgBSRGn (ORCPT ); Wed, 19 Feb 2020 12:06:43 -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=6hWL64aU7/cD1s4UTpPss89s1pka8CcWGCJ5BHjUC9M=; b=YD6KASfCXNzBE2g7U8C3OPAIMa RN+ihaDs+TqA1PVmJY/G+571Br5Ulv0XQc9EhsoYwQWJIGDt5eVY3v+7OW0ZDPPydpAvd+XANKK7o Yieli5fHS4G8IkuA6ZGWdtYi3uF69BcBtjkIg1txQfTuEC38FUNQpMva7d6LZIwTpJqOi2eTnjQ26 vNRvjsTCftaqhGEu3hEvctNIgYhTUrWaBzOu7hsE+5KmGRNAeS2s5R2DU2EMQh/fz/4XG6YC8Yfkl lb7zA1cZfGKpjcKVeyriFSjz0Jf9srJLBGVWu7kMAFznlMRG+bjJHweFWDFekIpMDNj5yFPnAlDOG rO8cGwug==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j4So6-00016p-If; Wed, 19 Feb 2020 17:06:42 +0000 Date: Wed, 19 Feb 2020 09:06:42 -0800 From: Matthew Wilcox To: Dave Chinner 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 v6 17/19] iomap: Restructure iomap_readpages_actor Message-ID: <20200219170642.GS24185@bombadil.infradead.org> References: <20200217184613.19668-1-willy@infradead.org> <20200217184613.19668-31-willy@infradead.org> <20200219032900.GE10776@dread.disaster.area> <20200219060415.GO24185@bombadil.infradead.org> <20200219064005.GL10776@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200219064005.GL10776@dread.disaster.area> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 19, 2020 at 05:40:05PM +1100, Dave Chinner wrote: > Ok, that's what the ctx.cur_page_in_bio check is used to detect i.e. > if we've got a page that the readahead cursor points at, and we > haven't actually added it to a bio, then we can leave it to the > read_pages() to unlock and clean up. If it's in a bio, then IO > completion will unlock it and so we only have to drop the submission > reference and move the readahead cursor forwards so read_pages() > doesn't try to unlock this page. i.e: > > /* clean up partial page submission failures */ > if (ctx.cur_page && ctx.cur_page_in_bio) { > put_page(ctx.cur_page); > readahead_next(rac); > } > > looks to me like it will handle the case of "ret == 0" in the actor > function just fine. Here's what I ended up with: @@ -400,15 +400,9 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length, void *data, struct iomap *iomap, struct iomap *srcmap) { struct iomap_readpage_ctx *ctx = data; - loff_t done, ret; - - for (done = 0; done < length; done += ret) { - if (ctx->cur_page && offset_in_page(pos + done) == 0) { - if (!ctx->cur_page_in_bio) - unlock_page(ctx->cur_page); - put_page(ctx->cur_page); - ctx->cur_page = NULL; - } + loff_t ret, done = 0; + + while (done < length) { if (!ctx->cur_page) { ctx->cur_page = iomap_next_page(inode, ctx->pages, pos, length, &done); @@ -418,6 +412,20 @@ iomap_readpages_actor(struct inode *inode, loff_t pos, loff_t length, } ret = iomap_readpage_actor(inode, pos + done, length - done, ctx, iomap, srcmap); + done += ret; + + /* Keep working on a partial page */ + if (ret && offset_in_page(pos + done)) + continue; + + if (!ctx->cur_page_in_bio) + unlock_page(ctx->cur_page); + put_page(ctx->cur_page); + ctx->cur_page = NULL; + + /* Don't loop forever if we made no progress */ + if (WARN_ON(!ret)) + break; } return done; @@ -451,11 +459,7 @@ iomap_readpages(struct address_space *mapping, struct list_head *pages, done: if (ctx.bio) submit_bio(ctx.bio); - if (ctx.cur_page) { - if (!ctx.cur_page_in_bio) - unlock_page(ctx.cur_page); - put_page(ctx.cur_page); - } + BUG_ON(ctx.cur_page); /* * Check that we didn't lose a page due to the arcance calling so we'll WARN if we get a ret == 0 (matching ->readpage), and we'll BUG if we ever see a page being leaked out of readpages_actor, which is a thing that should never happen and we definitely want to be noisy about if it does.