From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D6EB35CDF1; Wed, 15 Apr 2026 13:44:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776260661; cv=none; b=k2VOU+DjpZVluc17qgxYsZt/EZZpdWVw4yIJiU7L+q3nYNE7VX6IVzQYKTqqJ8auB50wOtnuFvKDU6Tr0WzVKyi50XfEtu5wHtOz1F6VlPd1ZzuK60Y5Rz7lOrRospK1mAIRHBPwGSgSynZkcuUhYgYrmN/iOQ5GTTw9lj8dMiM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776260661; c=relaxed/simple; bh=cvffzfRce8gu2XSdRh+/ukuCm0L1lipxNYSi9OVpUvA=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=thxmUhAwT5BkmfAdb9SRxWP1v72Ji3uNDp477UETnFOwHQqs9yv68d0IEQ8+mg2az6xWJhxLkTuf0Y6JQutSNKlMgjI3PYqqmpT1tko9iMo061VBqsWOnYCooZd388Y99kun2+ZHQAQKu6MJkmqLjHiaKqBtUVWrt6NOgocd/cQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=O14Y6OiI; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="O14Y6OiI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6615EC19424; Wed, 15 Apr 2026 13:44:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776260661; bh=cvffzfRce8gu2XSdRh+/ukuCm0L1lipxNYSi9OVpUvA=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=O14Y6OiIgOxRx33n/vdS+lVsD44z+ERugFSYtgWMWSXee4042fTPiRfFTuHs9lSwO keIScQk7WXJUHJMa6+uFSXaVn17d+ssN/RjYtfABSoX2LT827bw6XHklMdy+omRQOw lCuyktKDAvzDmOPZYCb8YhFwBP/MNVaFInDgMj2lA/rOAL4q1Fh6XWtXnqFS3Jg/7C H+BFVdGQbDPq5L819jQSK00oLg9hTzNHKGo2R65BD/w419Vywj3yHd/1uVro+hZrY5 wIsZXBsK0uWIN9KhxNwnWUlwPidpLg77oQNh1C6KF0pDZLkyVlF44FURCRzDHlId0C SyQ71XIZVdRbg== Message-ID: <9d8eda244e79b3b1c43c45277f225b130e88fa70.camel@kernel.org> Subject: Re: [LSF/MM/BPF TOPIC] Should we make inode->i_ino a u64? From: Jeff Layton To: John Paul Adrian Glaubitz , lsf-pc@lists.linux-foundation.org Cc: linux-fsdevel@vger.kernel.org, Christian Brauner , Christoph Hellwig , Jan Kara , Al Viro , linux-m68k , linux-sh Date: Wed, 15 Apr 2026 06:44:20 -0700 In-Reply-To: <1b340c4e635dcab3bed8c52d6381b4c341c0741a.camel@physik.fu-berlin.de> References: <08f8444c7237566ffb4ba8c9eb0ab4b4a5f14440.camel@kernel.org> <1b340c4e635dcab3bed8c52d6381b4c341c0741a.camel@physik.fu-berlin.de> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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bits on 32-bit CPUs, this has caused a lot of fs- > > specific hacks on filesystems that have native 64-bit inode numbers > > when running a 32-bit arch. > >=20 > > It would be a lot simpler if we just converted i_ino to be 64-bits and > > dealt with the conversion at the kernel's edges. This would be a non- > > event for the most part on 64-bit arches since unsigned long is already > > 64 bits there. > >=20 > > The kernel itself doesn't deal much with i_ino, so the internal changes > > look fairly straightforward. The bulk of the patches will be to format > > strings and to tracepoints. > >=20 > > I think that the biggest problem will be that this will grow struct > > inode on 32-bit arches by at least 4 bytes. That may have cacheline > > alignment and slab sizing implications. We're actively talking about > > deprecating 32-bit arches in the future however, so maybe we can > > rationalize that away. > >=20 > > FWIW, I had Claude spin up a plan to do this (attached). It's not bad. > > I'm tempted to tell it generate patches for this, since this is mostly > > a mechanical change, but I'm curious whether anyone else might have > > reasons that we shouldn't go ahead and do it. >=20 > So, this went just over Phoronix [1] and as someone who is still invested > in 32-bit architectures, I'm only notified about the performance impact o= n > these systems now as the pull request has already been sent to Linus. >=20 > I'm frustrated by this poor communication style. If your change affects c= ertain > users negatively, it should be openly communicated to them on the appropr= iate > mailing lists so that they at least get to raise concerns. Disclosing the= se > news to a limited set of mailing lists only is not okay. >=20 > Thanks, > Adrian >=20 > > [1] https://www.phoronix.com/news/Linux-7.1-VFS-Kino-32-bit You're pointing me at Phoronix and complaining about clear communication? That headline is made to generate clicks. It doesn't represent the reality. The mention of potential performance impact on 32 bit hosts is entirely speculative and not likely to be measurable anywhere. I only mentioned it at all in the interest of full disclosure. We're widening the i_ino field from 32 to 64 bits on 32-bit hosts. This means that we're adding 4 more bytes to every inode there. Sounds bad right?=20 The reality is more complicated... struct inode is (almost) always embedded in another structure that contains the fs-specific fields for it. Many of those (nfs, xfs, etc.) have had to carry a separate 64 bit field to hold the "real" inode number since we couldn't count on i_ino being big enough on 32-bit arches. Those fields can now go away, and once they do, that will represent a 4-byte _reduction_ in size of the inode on those filesystems. So there are potential upsides here for 32-bit arches as well. The bottom line is that we add and remove fields in struct inode all the time. It grows and shrinks as we do this. This change will almost certainly not be measurable anywhere. --=20 Jeff Layton