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=-8.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 757C8C433DB for ; Tue, 9 Feb 2021 10:31:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CE0F064E6F for ; Tue, 9 Feb 2021 10:31:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CE0F064E6F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 2C3346B006E; Tue, 9 Feb 2021 05:31:10 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 24D2C6B006C; Tue, 9 Feb 2021 05:31:10 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 13B906B006E; Tue, 9 Feb 2021 05:31:10 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0162.hostedemail.com [216.40.44.162]) by kanga.kvack.org (Postfix) with ESMTP id F1CBE6B0005 for ; Tue, 9 Feb 2021 05:31:09 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id B5A3481C6 for ; Tue, 9 Feb 2021 10:31:09 +0000 (UTC) X-FDA: 77798361858.24.glue33_5e0e6c627606 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin24.hostedemail.com (Postfix) with ESMTP id 9D5021A4A0 for ; Tue, 9 Feb 2021 10:31:09 +0000 (UTC) X-HE-Tag: glue33_5e0e6c627606 X-Filterd-Recvd-Size: 7679 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf18.hostedemail.com (Postfix) with ESMTP for ; Tue, 9 Feb 2021 10:31:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1612866668; h=from:from: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; bh=l9NmyWsJuFC0/5JNGWNXSCR8ksDc6+RfyJhTiUXWtF4=; b=cP7Ffwcn94KYGGhejcako2+99FPSGQZSCw8tStO970N4DoHzMRylWbHfu5RrDDGqUChDO5 NHokAsh2+FKdQQ1z1JY7hG625oDAyVlXmFzf9j6V14TOiV2INiEWJENJN6oE/oa9LHZcFK JjSubyzjZdm4/lZoYGmog2IgF5MuVn0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-105-IIfTrpvSPlC2PvPZbsJlDQ-1; Tue, 09 Feb 2021 05:31:06 -0500 X-MC-Unique: IIfTrpvSPlC2PvPZbsJlDQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C379C107ACE4; Tue, 9 Feb 2021 10:31:01 +0000 (UTC) Received: from [10.36.113.141] (ovpn-113-141.ams2.redhat.com [10.36.113.141]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3559C17AE2; Tue, 9 Feb 2021 10:30:54 +0000 (UTC) Subject: Re: [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas From: David Hildenbrand To: Michal Hocko Cc: Mike Rapoport , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org References: <20210208211326.GV242749@kernel.org> <1F6A73CF-158A-4261-AA6C-1F5C77F4F326@redhat.com> <662b5871-b461-0896-697f-5e903c23d7b9@redhat.com> Organization: Red Hat GmbH Message-ID: Date: Tue, 9 Feb 2021 11:30:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 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 09.02.21 11:23, David Hildenbrand wrote: >>>> A lot of unevictable memory is a concern regardless of CMA/ZONE_MOVABLE. >>>> As I've said it is quite easy to land at the similar situation even with >>>> tmpfs/MAP_ANON|MAP_SHARED on swapless system. Neither of the two is >>>> really uncommon. It would be even worse that those would be allowed to >>>> consume both CMA/ZONE_MOVABLE. >>> >>> IIRC, tmpfs/MAP_ANON|MAP_SHARED memory >>> a) Is movable, can land in ZONE_MOVABLE/CMA >>> b) Can be limited by sizing tmpfs appropriately >>> >>> AFAIK, what you describe is a problem with memory overcommit, not with zone >>> imbalances (below). Or what am I missing? >> >> It can be problem for both. If you have just too much of shm (do not >> forget about MAP_SHARED|MAP_ANON which is much harder to size from an >> admin POV) then migrateability doesn't really help because you need a >> free memory to migrate. Without reclaimability this can easily become a >> problem. That is why I am saying this is not really a new problem. >> Swapless systems are not all that uncommon. > > I get your point, it's similar but still different. "no memory in the > system" vs. "plenty of unusable free memory available in the system". > > In many setups, memory for user space applications can go to > ZONE_MOVABLE just fine. ZONE_NORMAL etc. can be used for supporting user > space memory (e.g., page tables) and other kernel stuff. > > Like, have 4GB of ZONE_MOVABLE with 2GB of ZONE_NORMAL. Have an > application (database) that allocates 4GB of memory. Works just fine. > The zone ratio ends up being a problem for example with many processes > (-> many page tables). > > Not being able to put user space memory into the movable zone is a > special case. And we are introducing yet another special case here > (besides vfio, rdma, unmigratable huge pages like gigantic pages). > > With plenty of secretmem, looking at /proc/meminfo Total vs. Free can be > a big lie of how your system behaves. > >> >>>> One has to be very careful when relying on CMA or movable zones. This is >>>> definitely worth a comment in the kernel command line parameter >>>> documentation. But this is not a new problem. >>> >>> I see the following thing worth documenting: >>> >>> Assume you have a system with 2GB of ZONE_NORMAL/ZONE_DMA and 4GB of >>> ZONE_MOVABLE/CMA. >>> >>> Assume you make use of 1.5GB of secretmem. Your system might run into OOM >>> any time although you still have plenty of memory on ZONE_MOVAVLE (and even >>> swap!), simply because you are making excessive use of unmovable allocations >>> (for user space!) in an environment where you should not make excessive use >>> of unmovable allocations (e.g., where should page tables go?). >> >> yes, you are right of course and I am not really disputing this. But I >> would argue that 2:1 Movable/Normal is something to expect problems >> already. "Lowmem" allocations can easily trigger OOM even without secret >> mem in the picture. It all just takes to allocate a lot of GFP_KERNEL or >> even GFP_{HIGH}USER. Really, it is CMA/MOVABLE that are elephant in the >> room and one has to be really careful when relying on them. > > Right, it's all about what the setup actually needs. Sure, there are > cases where you need significantly more GFP_KERNEL/GFP_{HIGH}USER such > that a 2:1 ratio is not feasible. But I claim that these are corner cases. > > Secretmem gives user space the option to allocate a lot of > GFP_{HIGH}USER memory. If I am not wrong, "ulimit -a" tells me that each > application on F33 can allocate 16 GiB (!) of secretmem. Got to learn to do my math. It's 16 MiB - so as a default it's less dangerous than I thought! -- Thanks, David / dhildenb