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 X-Spam-Level: X-Spam-Status: No, score=-7.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5591CC433E2 for ; Thu, 3 Sep 2020 18:40:15 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 127E620709 for ; Thu, 3 Sep 2020 18:40:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 127E620709 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A1AC36B008C; Thu, 3 Sep 2020 14:40:14 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A4A86B0093; Thu, 3 Sep 2020 14:40:14 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 86AD46B0095; Thu, 3 Sep 2020 14:40:14 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 68F036B008C for ; Thu, 3 Sep 2020 14:40:14 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 246668248068 for ; Thu, 3 Sep 2020 18:40:14 +0000 (UTC) X-FDA: 77222615148.12.suit76_3111b9d270ab Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id E313B1801261F for ; Thu, 3 Sep 2020 18:40:13 +0000 (UTC) X-HE-Tag: suit76_3111b9d270ab X-Filterd-Recvd-Size: 9333 Received: from mga05.intel.com (mga05.intel.com [192.55.52.43]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Sep 2020 18:40:12 +0000 (UTC) IronPort-SDR: zC35seifowEvzBrUVjbVABaTLGFRGD26COU/j3/eekSAu809OmDqK2BT4WkFbqtWndIQcWLvoS 7WwUntxveB+w== X-IronPort-AV: E=McAfee;i="6000,8403,9733"; a="242460195" X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="242460195" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 11:40:10 -0700 IronPort-SDR: Nmpt0QWq5TLNvvwUIIxuxCkfx+1BkLd8GMbs0Pp4am5RxTGfk0PBa6hqSeM/pz9NAQkaSdu2Bw hmnlaAjRJFBA== X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="478155843" Received: from viveksh1-mobl.amr.corp.intel.com (HELO [10.212.108.191]) ([10.212.108.191]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 11:40:07 -0700 Subject: Re: [PATCH v7 3/3] mm: add a field to store names for private anonymous memory To: Colin Cross Cc: Kees Cook , Sumit Semwal , Andrew Morton , Linux-MM , lkml , Alexey Dobriyan , Jonathan Corbet , Mauro Carvalho Chehab , Michal Hocko , Alexey Gladkov , Matthew Wilcox , Jason Gunthorpe , "Kirill A . Shutemov" , Michel Lespinasse , =?UTF-8?Q?Michal_Koutn=c3=bd?= , Song Liu , Huang Ying , Vlastimil Babka , Yang Shi , chenqiwu , Mathieu Desnoyers , John Hubbard , Mike Christie , Bart Van Assche , Amit Pundir , Thomas Gleixner , Christian Brauner , Daniel Jordan , Adrian Reber , Nicolas Viennot , Al Viro , linux-fsdevel@vger.kernel.org, John Stultz , Pekka Enberg , Peter Zijlstra , Ingo Molnar , Oleg Nesterov , "Eric W. Biederman" , Jan Glauber , Rob Landley , Cyrill Gorcunov , David Rientjes , Hugh Dickins , Rik van Riel , Mel Gorman , Robin Holt , Shaohua Li , Johannes Weiner , Minchan Kim , Sasha Levin , "Serge E. Hallyn" References: <20200901161459.11772-1-sumit.semwal@linaro.org> <20200901161459.11772-4-sumit.semwal@linaro.org> <202009031031.D32EF57ED@keescook> <393be893-6379-8adb-217c-4064f5052702@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzShEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gPGRhdmVAc3I3MS5uZXQ+wsF7BBMBAgAlAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAUCTo3k0QIZAQAKCRBoNZUwcMmSsMO2D/421Xg8pimb9mPzM5N7khT0 2MCnaGssU1T59YPE25kYdx2HntwdO0JA27Wn9xx5zYijOe6B21ufrvsyv42auCO85+oFJWfE K2R/IpLle09GDx5tcEmMAHX6KSxpHmGuJmUPibHVbfep2aCh9lKaDqQR07gXXWK5/yU1Dx0r VVFRaHTasp9fZ9AmY4K9/BSA3VkQ8v3OrxNty3OdsrmTTzO91YszpdbjjEFZK53zXy6tUD2d e1i0kBBS6NLAAsqEtneplz88T/v7MpLmpY30N9gQU3QyRC50jJ7LU9RazMjUQY1WohVsR56d ORqFxS8ChhyJs7BI34vQusYHDTp6PnZHUppb9WIzjeWlC7Jc8lSBDlEWodmqQQgp5+6AfhTD kDv1a+W5+ncq+Uo63WHRiCPuyt4di4/0zo28RVcjtzlGBZtmz2EIC3vUfmoZbO/Gn6EKbYAn rzz3iU/JWV8DwQ+sZSGu0HmvYMt6t5SmqWQo/hyHtA7uF5Wxtu1lCgolSQw4t49ZuOyOnQi5 f8R3nE7lpVCSF1TT+h8kMvFPv3VG7KunyjHr3sEptYxQs4VRxqeirSuyBv1TyxT+LdTm6j4a mulOWf+YtFRAgIYyyN5YOepDEBv4LUM8Tz98lZiNMlFyRMNrsLV6Pv6SxhrMxbT6TNVS5D+6 UorTLotDZKp5+M7BTQRUY85qARAAsgMW71BIXRgxjYNCYQ3Xs8k3TfAvQRbHccky50h99TUY sqdULbsb3KhmY29raw1bgmyM0a4DGS1YKN7qazCDsdQlxIJp9t2YYdBKXVRzPCCsfWe1dK/q 66UVhRPP8EGZ4CmFYuPTxqGY+dGRInxCeap/xzbKdvmPm01Iw3YFjAE4PQ4hTMr/H76KoDbD cq62U50oKC83ca/PRRh2QqEqACvIH4BR7jueAZSPEDnzwxvVgzyeuhwqHY05QRK/wsKuhq7s UuYtmN92Fasbxbw2tbVLZfoidklikvZAmotg0dwcFTjSRGEg0Gr3p/xBzJWNavFZZ95Rj7Et db0lCt0HDSY5q4GMR+SrFbH+jzUY/ZqfGdZCBqo0cdPPp58krVgtIGR+ja2Mkva6ah94/oQN lnCOw3udS+Eb/aRcM6detZr7XOngvxsWolBrhwTQFT9D2NH6ryAuvKd6yyAFt3/e7r+HHtkU kOy27D7IpjngqP+b4EumELI/NxPgIqT69PQmo9IZaI/oRaKorYnDaZrMXViqDrFdD37XELwQ gmLoSm2VfbOYY7fap/AhPOgOYOSqg3/Nxcapv71yoBzRRxOc4FxmZ65mn+q3rEM27yRztBW9 AnCKIc66T2i92HqXCw6AgoBJRjBkI3QnEkPgohQkZdAb8o9WGVKpfmZKbYBo4pEAEQEAAcLB XwQYAQIACQUCVGPOagIbDAAKCRBoNZUwcMmSsJeCEACCh7P/aaOLKWQxcnw47p4phIVR6pVL e4IEdR7Jf7ZL00s3vKSNT+nRqdl1ugJx9Ymsp8kXKMk9GSfmZpuMQB9c6io1qZc6nW/3TtvK pNGz7KPPtaDzvKA4S5tfrWPnDr7n15AU5vsIZvgMjU42gkbemkjJwP0B1RkifIK60yQqAAlT YZ14P0dIPdIPIlfEPiAWcg5BtLQU4Wg3cNQdpWrCJ1E3m/RIlXy/2Y3YOVVohfSy+4kvvYU3 lXUdPb04UPw4VWwjcVZPg7cgR7Izion61bGHqVqURgSALt2yvHl7cr68NYoFkzbNsGsye9ft M9ozM23JSgMkRylPSXTeh5JIK9pz2+etco3AfLCKtaRVysjvpysukmWMTrx8QnI5Nn5MOlJj 1Ov4/50JY9pXzgIDVSrgy6LYSMc4vKZ3QfCY7ipLRORyalFDF3j5AGCMRENJjHPD6O7bl3Xo 4DzMID+8eucbXxKiNEbs21IqBZbbKdY1GkcEGTE7AnkA3Y6YB7I/j9mQ3hCgm5muJuhM/2Fr OPsw5tV/LmQ5GXH0JQ/TZXWygyRFyyI2FqNTx4WHqUn3yFj8rwTAU1tluRUYyeLy0ayUlKBH ybj0N71vWO936MqP6haFERzuPAIpxj2ezwu0xb1GjTk4ynna6h5GjnKgdfOWoRtoWndMZxbA z5cecg== Message-ID: <5d0358ab-8c47-2f5f-8e43-23b89d6a8e95@intel.com> Date: Thu, 3 Sep 2020 11:40:06 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Rspamd-Queue-Id: E313B1801261F X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 Content-Transfer-Encoding: quoted-printable 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 9/3/20 11:26 AM, Colin Cross wrote: >> FWIW, I don't have any objections to this. >> >> Refcounting strings was what I think I had the strongest reaction to >> back in the good old days of 2013. strdup() on split plus strcmp() on >> merge doesn't sound afwul to me, and it is darn straightforward. The >> biggest downside is probably kernel memory consumption. We should >> probably just think through whether having so many duplicates changes >> things materially. >> >> For instance, should/could we penalize a task's vm.max_map_count when >> it's using this mechanism? > Just to provide some concrete numbers, the ART process I examined > (https://pastebin.com/YNUTvZyz) had 280 named anonymous mappings using > a total of 6566 bytes for the names. There were only 63 unique names, > using 1925 bytes. On my personal usage device, there are currently a > total of 59769 named anonymous devices across all processes using > 1224119 bytes, 5843 of them unique using 121754 bytes. The vast > majority of the unique names are of the form "stack_and_tls:999", > which are dynamically allocated in the userspace process' heap. There > are only 132 names that do not contain stack_and_tls using 9540 bytes, > repeated 49938 times using 1030651 bytes (108x). Most of those are > constant strings, meaning the pointer is into the .rodata section of a > file mapping that is shared between all processes. Thanks for the data! That seems like totally reasonable memory consumption in the normal cases. I'm mostly concerned about the worst-case kernel memory consumption. It's a DoS if there's a big change to the amount of kernel memory a process can consume. For instance, each VMA is 192 bytes. If the name limit was, say, 4k, it makes the per-VMA kernel memory consumption go up by a factor of 20, which isn't nice. But, if it's, say 16 bytes, it's only a 10% increase over what each VMA consumes today. > Is fork a concern? It would have to strdup every name. Should be pretty easy to confirm the worst case experimentally. Create a process with ~64k VMAs, time the fork()s. Then do the same with 64k VMAs with the longest names set on each VMA. If you can't time a difference, you'll have a strong argument that someone with 10 of these things in a process won't notice.