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=-8.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 DBE86C4741F for ; Tue, 29 Sep 2020 08:46:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FFB7207F7 for ; Tue, 29 Sep 2020 08:46:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727897AbgI2Iq4 (ORCPT ); Tue, 29 Sep 2020 04:46:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:54800 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725355AbgI2Iq4 (ORCPT ); Tue, 29 Sep 2020 04:46:56 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2AE81ACA3; Tue, 29 Sep 2020 08:46:54 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id D591D1E12E9; Tue, 29 Sep 2020 10:46:53 +0200 (CEST) Date: Tue, 29 Sep 2020 10:46:53 +0200 From: Jan Kara To: "Matthew Wilcox (Oracle)" Cc: linux-mm@kvack.org, Andrew Morton , Hugh Dickins , William Kucharski , Johannes Weiner , Jan Kara , Yang Shi , Dave Chinner , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 04/12] mm/filemap: Add mapping_seek_hole_data Message-ID: <20200929084653.GC10896@quack2.suse.cz> References: <20200914130042.11442-1-willy@infradead.org> <20200914130042.11442-5-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200914130042.11442-5-willy@infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 14-09-20 14:00:34, Matthew Wilcox (Oracle) wrote: > Rewrite shmem_seek_hole_data() and move it to filemap.c. > > Signed-off-by: Matthew Wilcox (Oracle) ... > +/** > + * mapping_seek_hole_data - Seek for SEEK_DATA / SEEK_HOLE in the page cache. > + * @mapping: Address space to search. > + * @start: First byte to consider. > + * @end: Limit of search (exclusive). > + * @whence: Either SEEK_HOLE or SEEK_DATA. > + * > + * If the page cache knows which blocks contain holes and which blocks > + * contain data, your filesystem can use this function to implement > + * SEEK_HOLE and SEEK_DATA. This is useful for filesystems which are > + * entirely memory-based such as tmpfs, and filesystems which support > + * unwritten extents. > + * > + * Return: The requested offset on successs, or -ENXIO if @whence specifies > + * SEEK_DATA and there is no data after @start. There is an implicit hole > + * after @end - 1, so SEEK_HOLE returns @end if all the bytes between @start > + * and @end contain data. > + */ > +loff_t mapping_seek_hole_data(struct address_space *mapping, loff_t start, > + loff_t end, int whence) > +{ > + XA_STATE(xas, &mapping->i_pages, start >> PAGE_SHIFT); > + pgoff_t max = (end - 1) / PAGE_SIZE; > + bool seek_data = (whence == SEEK_DATA); > + struct page *page; > + > + if (end <= start) > + return -ENXIO; > + > + rcu_read_lock(); > + while ((page = xas_find_get_entry(&xas, max, XA_PRESENT))) { > + loff_t pos = xas.xa_index * PAGE_SIZE; OK, but for ordinary filesystems this could be problematic because of exceptional entries? Also for shmem you've dropped the PageUptodate check which I'm not sure is safe? Honza -- Jan Kara SUSE Labs, CR