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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 61A81D12D72 for ; Mon, 11 Nov 2024 05:42:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9bCh2K1tspn+QQTLxt908qGwctHxFA/o2mvI8qgWAYQ=; b=XZ/avzA5GRUfgjeCa5EbfBXibB LYegB1zDYyeHGVPNrhTa1EqKAncsQcao79j9NFBRYcXBbsQCo9YLJv9SAarh8dVUCciVy3OWal2QD mAgzbO1d5mu7NvT1ep6oQxnu5/AvNQqKVyVOlV7sJw4u0EfBFRPrheGw466HDvUmH7piVmmtc9QeF bkCKrLJGd4Lay8af6Zu6dVX22TyRnsHjjt0TyIEGyl7EYHYbP5L2t/rwGFmVJmjRfCXDkgovRs6pG RRehLbXjR9puB8KOJmWo4nCEPx3JV6/Uh3C1sXxsYAVvBvM2bj5hPfj+sdE4IZx7XYyI4E4aXuKU4 ERWnz0zw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tANBl-0000000GPZp-3Rjt; Mon, 11 Nov 2024 05:42:13 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tANBh-0000000GPZE-2DBQ for linux-nvme@lists.infradead.org; Mon, 11 Nov 2024 05:42:11 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 1BFCF68C7B; Mon, 11 Nov 2024 06:42:00 +0100 (CET) Date: Mon, 11 Nov 2024 06:41:59 +0100 From: Christoph Hellwig To: Keith Busch Cc: Christoph Hellwig , Keith Busch , linux-nvme@lists.infradead.org, m@bjorling.me, matias.bjorling@wdc.com, kch@nvidia.com, kanie@linux.alibaba.com Subject: Re: [PATCHv4 13/13] nvmet: report ns's vwc not present Message-ID: <20241111054159.GA22853@lst.de> References: <20241107193849.995554-1-kbusch@meta.com> <20241107193849.995554-14-kbusch@meta.com> <20241108142743.GG6694@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241110_214209_832410_828E75C3 X-CRM114-Status: GOOD ( 17.99 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Fri, Nov 08, 2024 at 09:15:47AM -0700, Keith Busch wrote: > > > + if ((req->ns->file && !req->ns->buffered_io) || > > > > I don't think this check is correct. Direct I/O still requires cache > > flushes for durability. > > Oh, right. Would it be sufficient to check the file's block device for > write caching? > > if ((req->ns->file && !req->ns->buffered_io && > bdev_write_cache(file_inode(req->ns->file)->i_sb->s_bdev)) No, that's wrong for two reasons: 1) sb->s_bdev is only really relevant for mounting and st_dev reported in stat. It might not relate to where the file data is placed at all 2) the presence of cache in the underlying block device only has a minimal relation to the need to fdatasync a file you wrote to. Except for the corner case of overwritting a fully allocated (and not just preallocated) extent on an in-place write file system there always is metadata for a write that needs to be synchronized. You could work around that with an O_DYNC write that does that sync per I/O, but performance would be awful (and nvmet donsn't support that anyway)