From patchwork Fri Jun 16 09:26:39 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13282393 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 698C2EB64DB for ; Fri, 16 Jun 2023 09:31:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343748AbjFPJa5 (ORCPT ); Fri, 16 Jun 2023 05:30:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42878 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344291AbjFPJ3w (ORCPT ); Fri, 16 Jun 2023 05:29:52 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4771B4489 for ; Fri, 16 Jun 2023 02:28:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686907634; 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; bh=sl3/QLeGJaY8BoyaG/bUFRZ9MbEZGlLKStLHrswAEAI=; b=QkWmOzEolob5wPZ8R/h8tNNDSdAEDD3Nky2hZL4TsYYMQ/extFNlFlEKsj1hsbBRK+IReJ ND2vWKWXMNdHjdsB4ZeshiuA75qAN2qG25o3FQN9KIzN/2gMFfDnDse0HIxU0CEnUrNx3v qOCmb54nA8BPJIdJVlMRnQHIqMYE00g= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-70-W4J3JMR-PuWeRSpAjccIlA-1; Fri, 16 Jun 2023 05:27:09 -0400 X-MC-Unique: W4J3JMR-PuWeRSpAjccIlA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E9865800193; Fri, 16 Jun 2023 09:27:08 +0000 (UTC) Received: from t480s.fritz.box (unknown [10.39.194.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id D82E71121314; Fri, 16 Jun 2023 09:27:05 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Cc: David Hildenbrand , Paolo Bonzini , Igor Mammedov , Xiao Guangrong , "Michael S. Tsirkin" , Peter Xu , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Eduardo Habkost , Marcel Apfelbaum , Yanan Wang , Michal Privoznik , =?utf-8?q?Daniel_P_=2E_Berrang=C3=A9?= , Gavin Shan , Alex Williamson , kvm@vger.kernel.org Subject: [PATCH v1 00/15] virtio-mem: Expose device memory through multiple memslots Date: Fri, 16 Jun 2023 11:26:39 +0200 Message-Id: <20230616092654.175518-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org This is the follow-up on [1] that took longer than expected because vhost-user and other careless memslot consumers are just a pain. It's essentially a complete rewrite now that we have VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE (and I understood some nasty memslot details better), so no changelog. It's based on some cleanups [2, 3, 4] that are on the list. Quoting from patch #13: Having large virtio-mem devices that only expose little memory to a VM is currently a problem: we map the whole sparse memory region into the guest using a single memslot, resulting in one gigantic memslot in KVM. KVM allocates metadata for the whole memslot, which can result in quite some memory waste. Assuming we have a 1 TiB virtio-mem device and only expose little (e.g., 1 GiB) memory, we would create a single 1 TiB memslot and KVM has to allocate metadata for that 1 TiB memslot: on x86, this implies allocating a significant amount of memory for metadata: (1) RMAP: 8 bytes per 4 KiB, 8 bytes per 2 MiB, 8 bytes per 1 GiB -> For 1 TiB: 2147483648 + 4194304 + 8192 = ~ 2 GiB (0.2 %) With the TDP MMU (cat /sys/module/kvm/parameters/tdp_mmu) this gets allocated lazily when required for nested VMs (2) gfn_track: 2 bytes per 4 KiB -> For 1 TiB: 536870912 = ~512 MiB (0.05 %) (3) lpage_info: 4 bytes per 2 MiB, 4 bytes per 1 GiB -> For 1 TiB: 2097152 + 4096 = ~2 MiB (0.0002 %) (4) 2x dirty bitmaps for tracking: 2x 1 bit per 4 KiB page -> For 1 TiB: 536870912 = 64 MiB (0.006 %) So we primarily care about (1) and (2). The bad thing is, that the memory consumption *doubles* once SMM is enabled, because we create the memslot once for !SMM and once for SMM. Having a 1 TiB memslot without the TDP MMU consumes around: * With SMM: 5 GiB * Without SMM: 2.5 GiB Having a 1 TiB memslot with the TDP MMU consumes around: * With SMM: 1 GiB * Without SMM: 512 MiB ... and that's really something we want to optimize, to be able to just start a VM with small boot memory (e.g., 4 GiB) and a virtio-mem device that can grow very large (e.g., 1 TiB). Consequently, using multiple memslots and only mapping the memslots we really need can significantly reduce memory waste and speed up memslot-related operations. Let's expose the sparse RAM memory region using multiple memslots, mapping only the memslots we currently need into our device memory region container. The feature has to be turned manually on ("multiple-memslots=on") for now. As virtio-mem will auto-detect the number of memslots to use based on the current memslot configuration (max 256 for all memory devices), it's suggested to: (1) Define vhost device before memory devices on the QEMU cmdline. This primarily applies to vhost-user devices. (2) Not hotplug vhost (especially vhost-user) devices that impose further memslot retsrictions. For example, hotplugging a vhost-user device might now fail because more memslots are getting ised. Once vhost-user supports more memslots (i.e., ~512 instead of 32) these restrictions no longer apply. I run some tests on x86_64, but have to do some more testing with vfio. Patch #1-#4 add a soft limit for memslots, based on the maximum number of memslots around. Patch #5-#7 add support for memory devices that statically consome multiple memslots. Patch #8-#9 add support for memory devices that dynamically consume memslots on demand. Patch #10-#11 adds support for memory devices that can auto-detect the number of memslots to use. Patch #12-#13 adds "multiple-memslots=on" support to virtio-mem Patch #14-#15 make sure that virtio-mem memslots can be enabled/disable atomically [1] https://lkml.kernel.org/r/20211013103330.26869-1-david@redhat.com [2] https://lkml.kernel.org/r/20230523185915.540373-1-david@redhat.com [3] https://lkml.kernel.org/r/20230530113838.257755-1-david@redhat.com [4] https://lkml.kernel.org/r/20230523183036.517957-1-david@redhat.com Cc: Paolo Bonzini Cc: Igor Mammedov Cc: Xiao Guangrong Cc: "Michael S. Tsirkin" Cc: Peter Xu Cc: "Philippe Mathieu-Daudé" Cc: Eduardo Habkost Cc: Marcel Apfelbaum Cc: Yanan Wang Cc: Michal Privoznik Cc: Daniel P. Berrangé Cc: Gavin Shan Cc: Alex Williamson Cc: kvm@vger.kernel.org David Hildenbrand (15): memory-device: Track the required memslots in DeviceMemoryState kvm: Add stub for kvm_get_max_memslots() vhost: Add vhost_get_max_memslots() memory-device,vhost: Add a memslot soft limit for memory devices kvm: Return number of free memslots vhost: Return number of free memslots memory-device: Support memory devices that statically consume multiple memslots memory-device: Track the actually used memslots in DeviceMemoryState memory-device,vhost: Support memory devices that dynamically consume multiple memslots pc-dimm: Provide pc_dimm_get_free_slots() to query free ram slots memory-device: Support memory-devices with auto-detection of the number of memslots memory: Clarify mapping requirements for RamDiscardManager virtio-mem: Expose device memory via multiple memslots if enabled memory,vhost: Allow for marking memory device memory regions unmergeable virtio-mem: Mark memslot alias memory regions unmergeable accel/kvm/kvm-all.c | 35 +++-- accel/stubs/kvm-stub.c | 9 +- hw/mem/memory-device.c | 263 ++++++++++++++++++++++++++++++-- hw/mem/pc-dimm.c | 27 ++++ hw/virtio/vhost-stub.c | 9 +- hw/virtio/vhost.c | 41 ++++- hw/virtio/virtio-mem-pci.c | 21 +++ hw/virtio/virtio-mem.c | 271 ++++++++++++++++++++++++++++++++- include/exec/memory.h | 27 +++- include/hw/boards.h | 10 +- include/hw/mem/memory-device.h | 37 +++++ include/hw/mem/pc-dimm.h | 1 + include/hw/virtio/vhost.h | 3 +- include/hw/virtio/virtio-mem.h | 23 ++- include/sysemu/kvm.h | 4 +- include/sysemu/kvm_int.h | 1 + softmmu/memory.c | 35 ++++- stubs/qmp_memory_device.c | 15 ++ 18 files changed, 777 insertions(+), 55 deletions(-)