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=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 ECD85C2D0A3 for ; Tue, 3 Nov 2020 07:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB07B2222B for ; Tue, 3 Nov 2020 07:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727686AbgKCH5k (ORCPT ); Tue, 3 Nov 2020 02:57:40 -0500 Received: from verein.lst.de ([213.95.11.211]:36108 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725982AbgKCH5j (ORCPT ); Tue, 3 Nov 2020 02:57:39 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 3ABE167373; Tue, 3 Nov 2020 08:57:37 +0100 (CET) Date: Tue, 3 Nov 2020 08:57:36 +0100 From: Christoph Hellwig To: "Matthew Wilcox (Oracle)" Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, hch@lst.de, kent.overstreet@gmail.com Subject: Re: [PATCH 14/17] mm/filemap: Restructure filemap_get_pages Message-ID: <20201103075736.GM8389@lst.de> References: <20201102184312.25926-1-willy@infradead.org> <20201102184312.25926-15-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201102184312.25926-15-willy@infradead.org> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Nov 02, 2020 at 06:43:09PM +0000, Matthew Wilcox (Oracle) wrote: > Avoid a goto, and by the time we get to calling filemap_update_page(), > we definitely have at least one page. I find the error handling flow hard to follow and the existing but heavily touched naming of the nr_got variable and the find_pages label not helpful. I'd do the following on top of this patch: diff --git a/mm/filemap.c b/mm/filemap.c index f16b1eb03bcad0..3ef73a58ce9456 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2344,51 +2344,54 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter, pgoff_t index = iocb->ki_pos >> PAGE_SHIFT; pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT; struct page *page; - int nr_got, err = 0; + int nr_pages, err = 0; nr = min_t(unsigned long, last_index - index, nr); -find_page: +retry: if (fatal_signal_pending(current)) return -EINTR; - nr_got = mapping_get_read_thps(mapping, index, nr, pages); - if (!nr_got) { + nr_pages = mapping_get_read_thps(mapping, index, nr, pages); + if (!nr_pages) { if (iocb->ki_flags & IOCB_NOIO) return -EAGAIN; page_cache_sync_readahead(mapping, ra, filp, index, last_index - index); - nr_got = mapping_get_read_thps(mapping, index, nr, pages); + nr_pages = mapping_get_read_thps(mapping, index, nr, pages); } - if (!nr_got) { + if (!nr_pages) { if (iocb->ki_flags & (IOCB_NOWAIT | IOCB_WAITQ)) return -EAGAIN; pages[0] = filemap_create_page(filp, mapping, iocb->ki_pos >> PAGE_SHIFT); if (!pages[0]) - goto find_page; + goto retry; if (IS_ERR(pages[0])) return PTR_ERR(pages[0]); return 1; } - page = pages[nr_got - 1]; - if (PageReadahead(page)) + page = pages[nr_pages - 1]; + if (PageReadahead(page)) { err = filemap_readahead(iocb, filp, mapping, page, last_index); - if (!err && !PageUptodate(page)) + if (err) + goto error; + } + if (!PageUptodate(page)) { err = filemap_update_page(iocb, mapping, iter, page, - nr_got == 1); + nr_pages == 1); + if (err) + goto error; + } - if (err) - nr_got--; - if (likely(nr_got)) - return nr_got; - if (err < 0) - return err; - err = 0; - /* - * No pages and no error means we raced and should retry: - */ - goto find_page; + return nr_pages; + +error: + if (nr_pages > 1) + return nr_pages - 1; + if (err == AOP_TRUNCATED_PAGE) + goto retry; + return err; } /**