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 D5B56C7EE2A for ; Sat, 6 May 2023 00:08:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230374AbjEFAI1 (ORCPT ); Fri, 5 May 2023 20:08:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229803AbjEFAI0 (ORCPT ); Fri, 5 May 2023 20:08:26 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 60CD419B0; Fri, 5 May 2023 17:08:25 -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 EFD6563C72; Sat, 6 May 2023 00:08:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAD13C433EF; Sat, 6 May 2023 00:08:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1683331704; bh=7+4RZ/Snpwvb0zzhi2RjjXRKKk3ABC6o+jcKXRjDTg4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uJ4CUV1iru3AnzNtA79biymZMjwlHUzSgyfnsWmqGPjDok6TGCQSj9uC7b3O3oPJJ 7hYekNdQmu7P41mSRVxUZKoW7l4b2DBxXauxvQJ5VcutuHeMtpvZQrN2ZvYFBY8C0w cFwasIhIocEciWso+pgv0fKmhODCmMTdicFt3Zbm+IEEHYWZteSMzg5HUaEWh1wYsS n6woXHFNKHnn6crfiO3t2IWj/U18s5SnVAkRwJYqfkT4yzROMYiHzuA22rvffXunMJ gSApl7UVcU5tNNRz9aag+tq4sRGFtmNYW7vA1PrXzNDpkEpBxiGadFRA0LlgL6wbC/ NAGXWNH4WT4Sw== Date: Sat, 6 May 2023 00:08:22 +0000 From: Eric Biggers To: Dave Chinner Cc: John Garry , axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, martin.petersen@oracle.com, djwong@kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com, jejb@linux.ibm.com, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, Himanshu Madhani Subject: Re: [PATCH RFC 01/16] block: Add atomic write operations to request_queue limits Message-ID: References: <20230503183821.1473305-1-john.g.garry@oracle.com> <20230503183821.1473305-2-john.g.garry@oracle.com> <20230503213925.GD3223426@dread.disaster.area> <20230504222623.GI3223426@dread.disaster.area> <20230505233152.GN3223426@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230505233152.GN3223426@dread.disaster.area> Precedence: bulk List-ID: On Sat, May 06, 2023 at 09:31:52AM +1000, Dave Chinner wrote: > On Fri, May 05, 2023 at 10:47:19PM +0000, Eric Biggers wrote: > > On Fri, May 05, 2023 at 08:26:23AM +1000, Dave Chinner wrote: > > > > ok, we can do that but would also then make statx field 64b. I'm fine with > > > > that if it is wise to do so - I don't don't want to wastefully use up an > > > > extra 2 x 32b in struct statx. > > > > > > Why do we need specific varibles for DIO atomic write alignment > > > limits? We already have direct IO alignment and size constraints in statx(), > > > so why wouldn't we just reuse those variables when the user requests > > > atomic limits for DIO? > > > > > > i.e. if STATX_DIOALIGN is set, we return normal DIO alignment > > > constraints. If STATX_DIOALIGN_ATOMIC is set, we return the atomic > > > DIO alignment requirements in those variables..... > > > > > > Yes, we probably need the dio max size to be added to statx for > > > this. Historically speaking, I wanted statx to support this in the > > > first place because that's what we were already giving userspace > > > with XFS_IOC_DIOINFO and we already knew that atomic IO when it came > > > along would require a bound maximum IO size much smaller than normal > > > DIO limits. i.e.: > > > > > > struct dioattr { > > > __u32 d_mem; /* data buffer memory alignment */ > > > __u32 d_miniosz; /* min xfer size */ > > > __u32 d_maxiosz; /* max xfer size */ > > > }; > > > > > > where d_miniosz defined the alignment and size constraints for DIOs. > > > > > > If we simply document that STATX_DIOALIGN_ATOMIC returns minimum > > > (unit) atomic IO size and alignment in statx->dio_offset_align (as > > > per STATX_DIOALIGN) and the maximum atomic IO size in > > > statx->dio_max_iosize, then we don't burn up anywhere near as much > > > space in the statx structure.... > > > > I don't think that's how statx() is meant to work. The request mask is a bitmask, and the user can > > request an arbitrary combination of different items. For example, the user could request both > > STATX_DIOALIGN and STATX_WRITE_ATOMIC at the same time. That doesn't work if different items share > > the same fields. > > Sure it does - what is contained in the field on return is defined > by the result mask. In this case, whatever the filesystem puts in > the DIO fields will match which flag it asserts in the result mask. > > i.e. if the application wants RWF_ATOMIC and so asks for STATX_DIOALIGN | > STATX_DIOALIGN_ATOMIC in the request mask then: > > - if the filesystem does not support RWF_ATOMIC it fills in the > normal DIO alingment values and puts STATX_DIOALIGN in the result > mask. > > Now the application knows that it can't use RWF_ATOMIC, and it > doesn't need to do another statx() call to get the dio alignment > values it needs. > > - if the filesystem supports RWF_ATOMIC, it fills in the values with > the atomic DIO constraints and puts STATX_DIOALIGN_ATOMIC in the > result mask. > > Now the application knows it can use RWF_ATOMIC and has the atomic > DIO constraints in the dio alignment fields returned. > > This uses the request/result masks exactly as intended, yes? > We could certainly implement some scheme like that, but I don't think that was how statx() was intended to work. I think that each bit in the mask was intended to correspond to an independent piece of information. - Eric