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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A823AC433F5 for ; Fri, 20 May 2022 11:52:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348776AbiETLws (ORCPT ); Fri, 20 May 2022 07:52:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35972 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348762AbiETLwp (ORCPT ); Fri, 20 May 2022 07:52:45 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F31F615E48E; Fri, 20 May 2022 04:52:44 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 4FFC461DEB; Fri, 20 May 2022 11:52:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3BDA2C385A9; Fri, 20 May 2022 11:52:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653047563; bh=KjobZP6O6Jgwt6QhmllP83ZeT6Jg+VwnOafaxcAZ+8c=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=bptv6Mg3TVFF3Sk1DQV4g4ILT2blHfHJLQtoU4tvyhqF7sBMSi7SFHPt3GYix9zDj fmabFBKLLAt+mzYpio3Dnr/a7b1Bzz/E1lwcSx8VAf8RLyOdKVCKRepQRXrq4mW3NI xqhUOLKtCR6bJJICVsEgK6en7zdhRbI3TuWM4uIQLCEtyDzROd1z4XU0U6Eg3HnHGC 6Vu5Fs1CZPey2sZjUfEvTvZXyBNZShJ6tvoIR9/5uN7AJh/Mv7cAPeyxtXUC8GLCOr f3oZpQCpTLgA7aCs25q+jmOHsq0cBJOc1BrqKgBXL2hPTHR0+nkHa+zQP+BSejsGZ5 JQb/K98Kky8rA== Date: Fri, 20 May 2022 13:52:37 +0200 From: Christian Brauner To: Eric Biggers Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-xfs@vger.kernel.org, linux-api@vger.kernel.org, linux-fscrypt@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Keith Busch Subject: Re: [RFC PATCH v2 1/7] statx: add I/O alignment information Message-ID: <20220520115237.w2oa5bdzyzhkgwin@wittgenstein> References: <20220518235011.153058-1-ebiggers@kernel.org> <20220518235011.153058-2-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20220518235011.153058-2-ebiggers@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, May 18, 2022 at 04:50:05PM -0700, Eric Biggers wrote: > From: Eric Biggers > > Traditionally, the conditions for when DIO (direct I/O) is supported > were fairly simple: filesystems either supported DIO aligned to the > block device's logical block size, or didn't support DIO at all. > > However, due to filesystem features that have been added over time (e.g, > data journalling, inline data, encryption, verity, compression, > checkpoint disabling, log-structured mode), the conditions for when DIO > is allowed on a file have gotten increasingly complex. Whether a > particular file supports DIO, and with what alignment, can depend on > various file attributes and filesystem mount options, as well as which > block device(s) the file's data is located on. > > XFS has an ioctl XFS_IOC_DIOINFO which exposes this information to > applications. However, as discussed > (https://lore.kernel.org/linux-fsdevel/20220120071215.123274-1-ebiggers@kernel.org/T/#u), > this ioctl is rarely used and not known to be used outside of > XFS-specific code. It also was never intended to indicate when a file > doesn't support DIO at all, and it only exposes the minimum I/O > alignment, not the optimal I/O alignment which has been requested too. > > Therefore, let's expose this information via statx(). Add the > STATX_IOALIGN flag and three fields associated with it: > > * stx_mem_align_dio: the alignment (in bytes) required for user memory > buffers for DIO, or 0 if DIO is not supported on the file. > > * stx_offset_align_dio: the alignment (in bytes) required for file > offsets and I/O segment lengths for DIO, or 0 if DIO is not supported > on the file. This will only be nonzero if stx_mem_align_dio is > nonzero, and vice versa. > > * stx_offset_align_optimal: the alignment (in bytes) suggested for file > offsets and I/O segment lengths to get optimal performance. This > applies to both DIO and buffered I/O. It differs from stx_blocksize > in that stx_offset_align_optimal will contain the real optimum I/O > size, which may be a large value. In contrast, for compatibility > reasons stx_blocksize is the minimum size needed to avoid page cache > read/write/modify cycles, which may be much smaller than the optimum > I/O size. For more details about the motivation for this field, see > https://lore.kernel.org/r/20220210040304.GM59729@dread.disaster.area > > Note that as with other statx() extensions, if STATX_IOALIGN isn't set > in the returned statx struct, then these new fields won't be filled in. > This will happen if the filesystem doesn't support STATX_IOALIGN, or if > the file isn't a regular file. (It might be supported on block device > files in the future.) It might also happen if the caller didn't include > STATX_IOALIGN in the request mask, since statx() isn't required to > return information that wasn't requested. > > This commit adds the VFS-level plumbing for STATX_IOALIGN. Individual > filesystems will still need to add code to support it. > > Signed-off-by: Eric Biggers > --- Looks good to me, Reviewed-by: Christian Brauner (Microsoft)