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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 86D47C433E0 for ; Mon, 22 Feb 2021 14:54:52 +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 C995F64DE9 for ; Mon, 22 Feb 2021 14:54:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C995F64DE9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:42516 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lECbq-0001Ca-HN for qemu-devel@archiver.kernel.org; Mon, 22 Feb 2021 09:54:50 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:52658) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lECbA-0000fv-0C for qemu-devel@nongnu.org; Mon, 22 Feb 2021 09:54:08 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:40991) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lECb7-0000v8-9v for qemu-devel@nongnu.org; Mon, 22 Feb 2021 09:54:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614005643; 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=UstpoUaxTmjhMztIoL+/Nlb27xGxDLbniqc6VDm8cxM=; b=RNQR0aj5sD1oQuvr+r/x4Cw9iHI09AX3DdOtLIYQVytvfYi8rBUroKRNnAm/kTH++fiwry FNr2ofHnnBVsSBA63pb9cMEAo2ySLyP73cDFAZY2VGIVKKG4/BuJeNXCJ/JPyejwN8ZDCZ AOTe1QVX+DODm7anEauPYDzAuqu/O7Y= 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-416-k9SocQK-ND6osYplDD89qw-1; Mon, 22 Feb 2021 09:54:00 -0500 X-MC-Unique: k9SocQK-ND6osYplDD89qw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 93337AFA89; Mon, 22 Feb 2021 14:53:50 +0000 (UTC) Received: from [10.36.115.16] (ovpn-115-16.ams2.redhat.com [10.36.115.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 45C141F42F; Mon, 22 Feb 2021 14:53:47 +0000 (UTC) To: Paolo Bonzini , qemu-devel@nongnu.org References: <20210222115708.7623-1-david@redhat.com> <20210222115708.7623-2-david@redhat.com> <7137d1ad-2741-7536-5a3c-58d0c4f8306b@redhat.com> <0277759d-bb9a-6bf3-0ca4-53d3f7ec98f5@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Subject: Re: [PATCH v6 01/12] memory: Introduce RamDiscardMgr for RAM memory regions Message-ID: <24562156-457f-90b5-dcaf-c55fba1e881b@redhat.com> Date: Mon, 22 Feb 2021 15:53:45 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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 Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=david@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, 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: Pankaj Gupta , Wei Yang , "Michael S . Tsirkin" , Alex Williamson , Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , Pankaj Gupta , teawater , Igor Mammedov , Marek Kedzierski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 22.02.21 15:18, Paolo Bonzini wrote: > On 22/02/21 15:03, David Hildenbrand wrote: >> >>>> +    /** >>>> +     * @replay_populated: >>>> +     * >>>> +     * Notify the #RamDiscardListener about all populated parts >>>> within the >>>> +     * #MemoryRegion via the #RamDiscardMgr. >>>> +     * >>>> +     * In case any notification fails, no further notifications are >>>> triggered. >>>> +     * The listener is not required to be registered. >>>> +     * >>>> +     * @rdm: the #RamDiscardMgr >>>> +     * @mr: the #MemoryRegion >>>> +     * @rdl: the #RamDiscardListener >>>> +     * >>>> +     * Returns 0 on success, or a negative error if any notification >>>> failed. >>>> +     */ >>>> +    int (*replay_populated)(const RamDiscardMgr *rdm, const >>>> MemoryRegion *mr, >>>> +                            RamDiscardListener *rdl); >>> >>> If this function is only going to use a single callback, just pass it >>> (together with a void *opaque) as the argument. >>>> +}; >>>> + >>>>   typedef struct CoalescedMemoryRange CoalescedMemoryRange; >>>>   typedef struct MemoryRegionIoeventfd MemoryRegionIoeventfd; >>>> @@ -487,6 +683,7 @@ struct MemoryRegion { >>>>       const char *name; >>>>       unsigned ioeventfd_nb; >>>>       MemoryRegionIoeventfd *ioeventfds; >>>> +    RamDiscardMgr *rdm; /* Only for RAM */ >>>>   }; >>> >>> >>> The idea of sending discard notifications is obviously good.  I have a >>> couple of questions on the design that you used for the interface; I'm >>> not saying that it should be done differently, I would only like to >>> understand the trade offs that you chose: >> >> Sure! >> >>> >>> 1) can the RamDiscardManager (no abbreviations :)) be just the owner of >> >> I used to call it "SparseRamManager", but wanted to stress the semantics >> - and can use RamDiscardManager ;) . Suggestions welcome. >> >>> the memory region (obj->parent)?  Alternatively, if you want to make it >>> separate from the owner, does it make sense for it to be a separate >>> reusable object, sitting between virtio-mem and the MemoryRegion, so >>> that the implementation can be reused? >> >> virtio-mem consumes a memory backend (e.g., memory-backend-ram). That >> one logically "ownes" the memory region (and thereby the RAMBlock). >> >> The memory backend gets assigned to virtio-mem. At that point, >> virtio-mem "owns" the memory backend. It will set itself as the >> RamDiscardsManager before mapping the memory region into system address >> space (whereby it will get exposed to the system). >> >> This flow made sense to me. Regarding "reusable object" - I think the >> only stuff we could fit in there would be e.g., maintaining the lists of >> notifiers. I'd rather wait until we actually have a second user to see >> what we can factor out. >> >> If you have any suggestion/preference, please let me know. >> >>> >>> 2) why have the new RamDiscardListener instead of just extending >>> MemoryListener? Conveniently, vfio already has a MemoryListener that can >> >> It behaves more like the IOMMU notifier in that regard. > > Yes, but does it behave more like the IOMMU notifier in other regards? > :) The IOMMU notifier is concerned with an iova concept that doesn't > exist at the MemoryRegion level, while RamDiscardListener works at the > (MemoryRegion, offset) level that can easily be represented by a > MemoryRegionSection. Using MemoryRegionSection might even simplify the > listener code. It's similarly concerned with rather small, lightweight updates I would say. > >>> be extended, and you wouldn't need the list of RamDiscardListeners. >>> There is already a precedent of replaying the current state when a >>> listener is added (see listener_add_address_space), so this is not >>> something different between ML and RDL. >> >> The main motivation is to let listener decide how it wants to handle the >> memory region. For example, for vhost, vdpa, kvm, ... I only want a >> single region, not separate ones for each and every populated range, >> punching out discarded ranges. Note that there are cases (i.e., >> anonymous memory), where it's even valid for the guest to read discarded >> memory. > > Yes, I agree with that. You would still have the same > region-add/region_nop/region_del callbacks for KVM and friends; on top > of that you would have region_populate/region_discard callbacks for VFIO. I see roughly how it could work, however, I am not sure yet if this is the right approach. I think instead of region_populate/region_discard we would want individual region_add/region_del when populating/discarding for all MemoryListeners that opt-in somehow (e.g., VFIO, dump-guest-memory, ...). Similarly, we would want to call log_sync()/log_clear() then only for these parts. But what happens when I populate/discard some memory? I don't want to trigger an address space transaction (begin()...region_nop()...commit()) - whenever I populate/discard memory (e.g., in 2 MB granularity). Especially not, if nothing might have changed for most other MemoryListeners. > > Populated regions would be replayed after region_add, while I don't > think it makes sense to have a region_discard_all callback before > region_discard. How would we handle vfio_listerner_log_sync()vfio_sync_dirty_bitmap()? -- Thanks, David / dhildenb