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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, 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 29839C636CB for ; Thu, 15 Jul 2021 22:28:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 146F0613C9 for ; Thu, 15 Jul 2021 22:28:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232126AbhGOWb3 (ORCPT ); Thu, 15 Jul 2021 18:31:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232063AbhGOWb0 (ORCPT ); Thu, 15 Jul 2021 18:31:26 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAFEBC06175F; Thu, 15 Jul 2021 15:28:31 -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:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=pNcRIzV0WfWPp30XWVZN7R6wll8SWE/xO2pHaU3Fz5Q=; b=lWA/47usW8dcIhsdbVQReIK3Et 0GpByjW+BnwwQh/GGIBKXu7vfa1UFXyt4ZUsvnXDDfyUaYkXh/1l3k4bKjut4He9RqR7BLGVMiM4K GiRPreg+YpBttafzA6SICrOqymN93mmXCwXW5G67AzGzTgrzlzGErq4THkT9o8mMPbI1/6f40GlsG +J9aFqgpFOASnEelIE/G5ICWvPQFw2nC1m8dUOLVyBhHA0GIvwXLdUVaV3BolYoBuxLsIiIUZHzVG i6xLypdklO0GQ0LIS1Q7AuBVtZ3ve8TgLE1NOtefqyZYws6Ifc2AfQCOI58pBTz456li9XEZrAmMB EJzZXvJA==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m49pW-003w3v-Kt; Thu, 15 Jul 2021 22:27:49 +0000 Date: Thu, 15 Jul 2021 23:27:42 +0100 From: Matthew Wilcox To: "Darrick J. Wong" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v14 090/138] block: Add bio_add_folio() Message-ID: References: <20210715033704.692967-1-willy@infradead.org> <20210715033704.692967-91-willy@infradead.org> <20210715205917.GC22357@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210715205917.GC22357@magnolia> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 15, 2021 at 01:59:17PM -0700, Darrick J. Wong wrote: > On Thu, Jul 15, 2021 at 04:36:16AM +0100, Matthew Wilcox (Oracle) wrote: > > This is a thin wrapper around bio_add_page(). The main advantage here > > is the documentation that the submitter can expect to see folios in the > > completion handler, and that stupidly large folios are not supported. > > It's not currently possible to allocate stupidly large folios, but if > > it ever becomes possible, this function will fail gracefully instead of > > doing I/O to the wrong bytes. > > > > Signed-off-by: Matthew Wilcox (Oracle) > > --- > > block/bio.c | 21 +++++++++++++++++++++ > > include/linux/bio.h | 3 ++- > > 2 files changed, 23 insertions(+), 1 deletion(-) > > > > diff --git a/block/bio.c b/block/bio.c > > index 1fab762e079b..1b500611d25c 100644 > > --- a/block/bio.c > > +++ b/block/bio.c > > @@ -933,6 +933,27 @@ int bio_add_page(struct bio *bio, struct page *page, > > } > > EXPORT_SYMBOL(bio_add_page); > > > > +/** > > + * bio_add_folio - Attempt to add part of a folio to a bio. > > + * @bio: Bio to add to. > > + * @folio: Folio to add. > > + * @len: How many bytes from the folio to add. > > + * @off: First byte in this folio to add. > > + * > > + * Always uses the head page of the folio in the bio. If a submitter > > + * only uses bio_add_folio(), it can count on never seeing tail pages > > + * in the completion routine. BIOs do not support folios larger than 2GiB. > > + * > > + * Return: The number of bytes from this folio added to the bio. > > + */ > > +size_t bio_add_folio(struct bio *bio, struct folio *folio, size_t len, > > + size_t off) > > +{ > > + if (len > UINT_MAX || off > UINT_MAX) > > Er... if bios don't support folios larger than 2GB, then why check @off > and @len against UINT_MAX, which is ~4GB? I suppose that's mostly a documentation problem. The limit is: struct bio_vec { struct page *bv_page; unsigned int bv_len; unsigned int bv_offset; }; so we can support folios which are 2GB in size (0x8000'0000) bytes, but if (theoretically, some day) we had a 4GB folio, we wouldn't be able to handle it in a single bio_vec. So there isn't anything between a 2GB folio and a 4GB folio; a 4GB folio isn't allowed and a 2GB one is. I don't think anything's wrong here, but maybe things could be worded better?