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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id b2sm5837535qtg.88.2021.11.23.05.25.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Nov 2021 05:25:24 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mpVnX-0001kU-Up; Tue, 23 Nov 2021 09:25:23 -0400 Date: Tue, 23 Nov 2021 09:25:23 -0400 From: Jason Gunthorpe To: David Hildenbrand Cc: 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: <20211123132523.GA5112@ziepe.ca> References: <20211115203530.62ff33fdae14927b48ef6e5f@linux-foundation.org> <20211116114727.601021d0763be1f1efe2a6f9@linux-foundation.org> <20211116133750.0f625f73a1e4843daf13b8f7@linux-foundation.org> <8f219a64-a39f-45f0-a7ad-708a33888a3b@www.fastmail.com> <333cb52b-5b02-648e-af7a-090e23261801@redhat.com> <5f998bb7-7b5d-9253-2337-b1d9ea59c796@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5f998bb7-7b5d-9253-2337-b1d9ea59c796@redhat.com> X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: AE8F14002091 X-Stat-Signature: 45mxj11omo1oq6ssic1hkjpmupdr6enx Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=ziepe.ca header.s=google header.b=ZAIcvL7Q; spf=pass (imf18.hostedemail.com: domain of jgg@ziepe.ca designates 209.85.219.48 as permitted sender) smtp.mailfrom=jgg@ziepe.ca; dmarc=none X-HE-Tag: 1637673924-667008 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 Mon, Nov 22, 2021 at 09:08:47PM +0100, David Hildenbrand wrote: > > You can't use mmu notifiers without impacting the fast path. This isn't > > just about io_uring, there are other users of memlock right now (like > > bpf) which just makes it even worse. > > 1) Do we have a performance evaluation? Did someone try and come up with > a conclusion how bad it would be? It needs additional locking between page readers and the mmu notifier. One of the virtio things does this thing and they used rcu on the page readers and a synchronize rcu in a mmu notifier - which I think is pretty bad. > 2) Could be provide a mmu variant to ordinary users that's just good > enough but maybe not as fast as what we have today? And limit > FOLL_LONGTERM to special, privileged users? rdma has never been privileged Jason