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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 67EBCCE7B19 for ; Thu, 28 Sep 2023 18:02:01 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E2C196B00E5; Thu, 28 Sep 2023 14:02:00 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DB3BF6B00ED; Thu, 28 Sep 2023 14:02:00 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BDF6B6B00FE; Thu, 28 Sep 2023 14:02:00 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id AD7CB6B00E5 for ; Thu, 28 Sep 2023 14:02:00 -0400 (EDT) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 605C1C0F6F for ; Thu, 28 Sep 2023 18:02:00 +0000 (UTC) X-FDA: 81286774800.15.B02066D Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by imf18.hostedemail.com (Postfix) with ESMTP id 37DB71C003C for ; Thu, 28 Sep 2023 18:01:51 +0000 (UTC) Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bfK28RLd; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf18.hostedemail.com: domain of jlayton@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=jlayton@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1695924112; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=EAdPFsmHcyWayc69u1pNQGVN/Od37LMkwOOQtSvFBiM=; b=Iw4t1c9qy5j7OaGhTGe93rWNARsEwOKpa09W+TxUH+O+U/E/ZQCxmSUN7sGR+hp33K9HPi Jk7ICby+K6+CXaPlhNHxfaiCTW1JE5GUInNO4I+t1aPd0NGS5k5QdAj1Y05oi15ZCy1vD5 JXTj9GiSIPHaI2xw0jB36oEn2RZdEvU= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=bfK28RLd; dmarc=pass (policy=none) header.from=kernel.org; spf=pass (imf18.hostedemail.com: domain of jlayton@kernel.org designates 145.40.68.75 as permitted sender) smtp.mailfrom=jlayton@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1695924112; a=rsa-sha256; cv=none; b=k8b6+LO5Wts14Ik/3d81/3GQvN3lWuny5oskjfcz6UAcHZDX8zQZQcArqTSW9hQhqptZkC H1AND5j4IeG1fhjCUF8/b7CPdhzy9aGhq4Al5S0kHJrT5fgRjotVuZP58p45elmtAb91GE h8GUqkKELsYeMtZk+x0tYBY4aYUHpMM= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by ams.source.kernel.org (Postfix) with ESMTP id D6EECB81DC1; Thu, 28 Sep 2023 18:01:49 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A6C1DC433C7; Thu, 28 Sep 2023 18:01:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1695924109; bh=EAdPFsmHcyWayc69u1pNQGVN/Od37LMkwOOQtSvFBiM=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=bfK28RLdLGgKZCUgDzeWTBKaqWs6brrGRaSyPdFXskOVm0On6PlLojE5M/xCgEEY5 grpUMo2uaqDtijMvKbHWfOGFJG+vQA/tkSyBcl6qHWL3dn3aU/KYO5L4q/l83Nz1PF rjm7ECl0slpI4oU4YRq3Il4iqcNMzLzfgVWdoz5lG6ZAiTp3N12KGI95ZvFcFMlTR+ jbG318WOr9JpuRBEryTb1XBxjEr4Jw9k8E4/FfV1BqWFd1k5jtZEs5n6naq0zoe6ze HRJ/cpQFseJro5/YEKgl8SVwodWHkLRLpC8H6rkjRLoCIio3JUF68vh6UiBMp7cQEp W7opbVnaB1VbA== Message-ID: <00ca2e3997cc86401f7fb65d936fe5403abd5627.camel@kernel.org> Subject: Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode From: Jeff Layton To: Linus Torvalds Cc: Alexander Viro , Christian Brauner , David Sterba , Amir Goldstein , Theodore Ts'o , Eric Biederman , Kees Cook , Jeremy Kerr , Arnd Bergmann , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Greg Kroah-Hartman , Arve =?ISO-8859-1?Q?Hj=F8nnev=E5g?= , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Mattia Dongili , Dennis Dalessandro , Jason Gunthorpe , Leon Romanovsky , Brad Warrum , Ritu Agarwal , Hans de Goede , Ilpo =?ISO-8859-1?Q?J=E4rvinen?= , Mark Gross , Jiri Slaby , Eric Van Hensbergen , Latchesar Ionkov , Dominique Martinet , Christian Schoenebeck , David Sterba , David Howells , Marc Dionne , Ian Kent , Luis de Bethencourt , Salah Triki , "Tigran A. 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T3Cko3Edlmxo/rmRbzjWTQqveTS9R7PCJfBDLddnphmGn/bEawdov+J8sqBm85T+HvxScOq2vKxLh+dhKJUjtb3kyeJDCvkdgvvK5DEYX4dTb0JWAjWxsxbnO4Y5oixP+YtpFV1lZhKtXMllucMuV96OlmLIbdbDBwPOFqENRV8eE6mad+LBxO0Ai5iMeZImimEAuC9FlVovFpyyTrEh+5jVqPxZgPVR2B39dYhT6Uw3tTHmwZJXaCWJv3VAYNAOFW1HDYnFZYZv134zAACWzekNb+p9HpkvoeIWkLT2zQH/49R96FEzsKKFdzfHmRCfIVarF7FqhWH3Qc8kMVo6DF+RIf6H4o6K0W3/MD5p6LpTktQxHakp4IT9I47+BRo5rjkzxP8K5BgQAIk8PYbMj7y6vjtYvkMjA= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, 2023-09-28 at 10:41 -0700, Linus Torvalds wrote: > On Thu, 28 Sept 2023 at 04:06, Jeff Layton wrote: > >=20 > > Move i_blocks up above the i_lock, which moves the new 4 byte hole to > > just after the timestamps, without changing the size of the structure. >=20 > I'm sure others have mentioned this, but 'struct inode' is marked with > __randomize_layout, so the actual layout may end up being very > different. >=20 > I'm personally not convinced the whole structure randomization is > worth it - it's easy enough to figure out for any distro kernel since > the seed has to be the same across machines for modules to work, so > even if the seed isn't "public", any layout is bound to be fairly > easily discoverable. >=20 > So the whole randomization only really works for private kernel > builds, and it adds this kind of pain where "optimizing" the structure > layout is kind of pointless depending on various options. >=20 > I certainly *hope* no distro enables that pointless thing, but it's a wor= ry. >=20 I've never enabled struct randomization and don't know anyone who does. I figure if you turn that on, you get to keep all of the pieces when you start seeing weird performance problems. I think that we have to optimize for that being disabled. Even without that though, turning on and off options can change the layout...and then there are different arches, etc. I'm using a config derived from the Fedora x86_64 kernel images and hope that represents a reasonably common configuration. The only conditional members before the timestamps are based on CONFIG_FS_POSIX_ACL and CONFIG_SECURITY, which are almost always turned on with most distros. --=20 Jeff Layton