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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id l22sm42040qtj.68.2021.11.24.07.34.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Nov 2021 07:34:06 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mpuHd-0013L9-Or; Wed, 24 Nov 2021 11:34:05 -0400 Date: Wed, 24 Nov 2021 11:34:05 -0400 From: Jason Gunthorpe To: David Hildenbrand Cc: Vlastimil Babka , Jens Axboe , Andrew Dona-Couch , Andrew Morton , Drew DeVault , Ammar Faizi , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, io_uring Mailing List , Pavel Begunkov , linux-mm@kvack.org Subject: Re: [PATCH] Increase default MLOCK_LIMIT to 8 MiB Message-ID: <20211124153405.GJ5112@ziepe.ca> References: <20211123170056.GC5112@ziepe.ca> <20211123235953.GF5112@ziepe.ca> <2adca04f-92e1-5f99-6094-5fac66a22a77@redhat.com> <20211124132353.GG5112@ziepe.ca> <20211124132842.GH5112@ziepe.ca> <20211124134812.GI5112@ziepe.ca> <2cdbebb9-4c57-7839-71ab-166cae168c74@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2cdbebb9-4c57-7839-71ab-166cae168c74@redhat.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: A3157F0001D5 X-Stat-Signature: 9wgyh9r37zr6obpx6dxb41u4a17sfbmr Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=WzvFRKZ0; dmarc=none; spf=pass (imf17.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.219.44 as permitted sender) smtp.mailfrom=jgg@ziepe.ca X-HE-Tag: 1637768050-274126 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 Wed, Nov 24, 2021 at 03:14:00PM +0100, David Hildenbrand wrote: > I'm not aware of any where you can fragment 50% of all pageblocks in the > system as an unprivileged user essentially consuming almost no memory > and essentially staying inside well-defined memlock limits. But sure if > there are "many" people will be able to come up with at least one > comparable thing. I'll be happy to learn. If the concern is that THP's can be DOS'd then any avenue that renders the system out of THPs is a DOS attack vector. Including all the normal workloads that people run and already complain that THPs get exhausted. A hostile userspace can only quicken this process. > My position that FOLL_LONGTERM for unprivileged users is a strong no-go > stands as it is. As this basically excludes long standing pre-existing things like RDMA, XDP, io_uring, and more I don't think this can be the general answer for mm, sorry. Sure, lets stop now since I don't think we can agree. Jason