From patchwork Fri Jul 30 08:52:42 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 12410639 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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 F0412C4338F for ; Fri, 30 Jul 2021 08:54:42 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 6D51160F6B for ; Fri, 30 Jul 2021 08:54:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6D51160F6B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:51550 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1m9OHx-0000Fq-DK for qemu-devel@archiver.kernel.org; Fri, 30 Jul 2021 04:54:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42102) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m9OGd-0006of-6N for qemu-devel@nongnu.org; Fri, 30 Jul 2021 04:53:19 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:59517) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1m9OGZ-0006rz-3E for qemu-devel@nongnu.org; Fri, 30 Jul 2021 04:53:17 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1627635193; 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=HLSztXQMqToB1EaxyuaDliCMwkbciIGVtYRqlXwAg3E=; b=X+ou5xy4nli4h9kj+GVeuP+ZmjhRB+1tY7FkSw+icCYSOFQZS+G5I8kL9AX9VFxPTnU4Xs J1VGYB1mOd7XxWWFStmk3tx6o250KyBEJykCBLukxLPffBJ1Is8BTwhCJ7AiAcb3JhHcCh 9e+NFe6zmhtu/FCHrlOCmNNqIhX8jvY= 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-500-UY89g_gFNIympnbmGzDJQQ-1; Fri, 30 Jul 2021 04:53:11 -0400 X-MC-Unique: UY89g_gFNIympnbmGzDJQQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4AB051008062; Fri, 30 Jul 2021 08:53:10 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.194.81]) by smtp.corp.redhat.com (Postfix) with ESMTP id AED8E60C05; Fri, 30 Jul 2021 08:52:50 +0000 (UTC) From: David Hildenbrand To: qemu-devel@nongnu.org Subject: [PATCH v3 0/7] migration/ram: Optimize for virtio-mem via RamDiscardManager Date: Fri, 30 Jul 2021 10:52:42 +0200 Message-Id: <20210730085249.8246-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=david@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=170.10.133.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.717, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Eduardo Habkost , "Michael S. Tsirkin" , Pankaj Gupta , Juan Quintela , David Hildenbrand , "Dr. David Alan Gilbert" , Peter Xu , Marek Kedzierski , Alex Williamson , teawater , Paolo Bonzini , Andrey Gruzdev , Wei Yang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" virtio-mem exposes a dynamic amount of memory within RAMBlocks by coordinating with the VM. Memory within a RAMBlock can either get plugged and consequently used by the VM, or unplugged and consequently no longer used by the VM. Logical unplug is realized by discarding the physical memory backing for virtual memory ranges, similar to memory ballooning. However, important difference to virtio-balloon are: a) A virtio-mem device only operates on its assigned memory region / RAMBlock ("device memory") b) Initially, all device memory is logically unplugged c) Virtual machines will never accidentally reuse memory that is currently logically unplugged. The spec defines most accesses to unplugged memory as "undefined behavior" -- except reading unplugged memory, which is currently expected to work, but that will change in the future. d) The (un)plug granularity is in the range of megabytes -- "memory blocks" e) The state (plugged/unplugged) of a memory block is always known and properly tracked. Whenever memory blocks within the RAMBlock get (un)plugged, changes are communicated via the RamDiscardManager to other QEMU subsystems, most prominently vfio which updates the DMA mapping accordingly. "Unplugging" corresponds to "discarding" and "plugging" corresponds to "populating". While migrating (precopy/postcopy) that state of such memory blocks cannot change, as virtio-mem will reject any guest requests that would change the state of blocks with "busy". We don't want to migrate such logically unplugged memory, because it can result in an unintended memory consumption both, on the source (when reading memory from some memory backends) and on the destination (when writing memory). Further, migration time can be heavily reduced when skipping logically unplugged blocks and we avoid populating unnecessary page tables in Linux. Right now, virtio-mem reuses the free page hinting infrastructure during precopy to exclude all logically unplugged ("discarded") parts from the migration stream. However, there are some scenarios that are not handled properly and need fixing. Further, there are some ugly corner cases in postcopy code and background snapshotting code that similarly have to handle such special RAMBlocks. Let's reuse the RamDiscardManager infrastructure to essentially handle precopy, postcopy and background snapshots cleanly, which means: a) In precopy code, fixing up the initial dirty bitmaps (in the RAMBlock and e.g., KVM) to exclude discarded ranges. b) In postcopy code, placing a zeropage when requested to handle a page falling into a discarded range -- because the source will never send it. Further, fix up the dirty bitmap when overwriting it in recovery mode. c) In background snapshot code, never populating discarded ranges, not even with the shared zeropage, to avoid unintended memory consumption, especially in the future with hugetlb and shmem. Detail: When realizing a virtio-mem devices, it will register the RAM for migration via vmstate_register_ram(). Further, it will set itself as the RamDiscardManager for the corresponding memory region of the RAMBlock via memory_region_set_ram_discard_manager(). Last but not least, memory device code will actually map the memory region into guest physical address space. So migration code can always properly identify such RAMBlocks. Tested with precopy/postcopy on shmem, where even reading unpopulated memory ranges will populate actual memory and not the shared zeropage. Tested with background snapshots on anonymous memory, because other backends are not supported yet with upstream Linux. Idealy, this should all go via the migration tree. v2 -> v3: - "migration/ram: Don't passs RAMState to migration_clear_memory_region_dirty_bitmap_*()" -- Added to make the next patch easier to implement - "migration/ram: Handle RAMBlocks with a RamDiscardManager on the migration source" -- Fixup the dirty bitmaps only initially and during postcopy recovery, not after every bitmap sync. Also properly clear the dirty bitmaps e.g., in KVM. [Peter] - "migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination" -- Take care of proper host-page alignment [Peter] v1 -> v2: - "migration/ram: Handle RAMBlocks with a RamDiscardManager on the migration source" -- Added a note how it interacts with the clear_bmap and what we might want to further optimize in the future when synchronizing bitmaps. Cc: "Michael S. Tsirkin" Cc: Paolo Bonzini Cc: Juan Quintela Cc: "Dr. David Alan Gilbert" Cc: Eduardo Habkost Cc: Peter Xu Cc: Andrey Gruzdev Cc: Marek Kedzierski Cc: Wei Yang Cc: teawater Cc: Alex Williamson Cc: Pankaj Gupta David Hildenbrand (7): memory: Introduce replay_discarded callback for RamDiscardManager virtio-mem: Implement replay_discarded RamDiscardManager callback migration/ram: Don't passs RAMState to migration_clear_memory_region_dirty_bitmap_*() migration/ram: Handle RAMBlocks with a RamDiscardManager on the migration source virtio-mem: Drop precopy notifier migration/postcopy: Handle RAMBlocks with a RamDiscardManager on the destination migration/ram: Handle RAMBlocks with a RamDiscardManager on background snapshots hw/virtio/virtio-mem.c | 92 +++++++++++------- include/exec/memory.h | 21 +++++ include/hw/virtio/virtio-mem.h | 3 - migration/postcopy-ram.c | 31 +++++- migration/ram.c | 166 +++++++++++++++++++++++++++++---- migration/ram.h | 1 + softmmu/memory.c | 11 +++ 7 files changed, 267 insertions(+), 58 deletions(-)