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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 530B2C433EF for ; Mon, 27 Sep 2021 19:26:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 352DE600EF for ; Mon, 27 Sep 2021 19:26:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236483AbhI0T2P (ORCPT ); Mon, 27 Sep 2021 15:28:15 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:36278 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236511AbhI0T2O (ORCPT ); Mon, 27 Sep 2021 15:28:14 -0400 Received: from relay1.suse.de (relay1.suse.de [149.44.160.133]) by smtp-out2.suse.de (Postfix) with ESMTP id BF9B31FF70; Mon, 27 Sep 2021 19:26:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1632770795; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=X7tJAlMOltgLYFO9ljBjewotozXZLEfuXLRh0kVD3Yc=; b=JQTmeIoe6/AbcDQfsXm2PpDbDyH5KYaElINWn2HxYoyRAgiR0O1Tm5ltWSWR5vwU0dwHd8 KKqQZUCkLtz47LmjPjDmZ+WBnlw2dZprWyIMX/YNf1/Ma+eE1ikSuouxZuKPcfp13Uyyc8 v09rVQTT3zaAd5GbRQJtEkRwcMk8iis= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1632770795; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=X7tJAlMOltgLYFO9ljBjewotozXZLEfuXLRh0kVD3Yc=; b=2WDuBAt4uYbVtGkufeKEwx00RL2WZBcFtGWOjDUx2N5QQ41WCLVZANai8tg4PVs9nkFn+9 /xhWooc+qLwURbDA== Received: from ds.suse.cz (ds.suse.cz [10.100.12.205]) by relay1.suse.de (Postfix) with ESMTP id 90A9625D3E; Mon, 27 Sep 2021 19:26:35 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id B2D85DA799; Mon, 27 Sep 2021 21:26:19 +0200 (CEST) Date: Mon, 27 Sep 2021 21:26:18 +0200 From: David Sterba To: Naohiro Aota Cc: linux-btrfs@vger.kernel.org, David Sterba Subject: Re: [PATCH 0/5] btrfs-progs: use direct-IO for zoned device Message-ID: <20210927192618.GF9286@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Naohiro Aota , linux-btrfs@vger.kernel.org, David Sterba References: <20210927041554.325884-1-naohiro.aota@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210927041554.325884-1-naohiro.aota@wdc.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Mon, Sep 27, 2021 at 01:15:49PM +0900, Naohiro Aota wrote: > As discussed in the Zoned Storage page [1], the kernel page cache does not > guarantee that cached dirty pages will be flushed to a block device in > sequential sector order. Thus, we must use O_DIRECT for writing to a zoned > device to ensure the write ordering. > > [1] https://zonedstorage.io/linux/overview/#zbd-support-restrictions > > As a writng buffer is embedded in some other struct (e.g., "char data[]" in > struct extent_buffer), it is difficult to allocate the struct so that the > writng buffer is aligned. > > This series introduces btrfs_{pread,pwrite} to wrap around pread/pwrite, > which allocates an aligned bounce buffer, copy the buffer contents, and > proceeds the IO. And, it now opens a zoned device with O_DIRECT. > > Since the allocation and copying are costly, it is better to do them only > when necessary. But, it is cumbersome to call fcntl(F_GETFL) to determine > the file is opened with O_DIRECT or not every time doing an IO. This should be in the changelog somewhere too, the last patch looks like a good place so I'll copy it there. > As zoned device forces to use zoned btrfs, I decided to use the zoned flag > to determine if it is direct-IO or not. This can cause a false-positive (to > use the bounce buffer when a file is *not* opened with O_DIRECT) in case of > emulated zoned mode on a non-zoned device or a regular file. Considering > the emulated zoned mode is mostly for debugging or testing, I believe this > is acceptable. Agreed. All patches added to devel. Would be good to add some tests for the emulated mode, ie. that we can test at least something regularly without special devices.