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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 32F77C63777 for ; Thu, 3 Dec 2020 10:08:47 +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 7108B20705 for ; Thu, 3 Dec 2020 10:08:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7108B20705 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]:42946 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kklXZ-0007l0-Cj for qemu-devel@archiver.kernel.org; Thu, 03 Dec 2020 05:08:45 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:34766) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kklWx-0007LH-G4 for qemu-devel@nongnu.org; Thu, 03 Dec 2020 05:08:07 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:42408) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kklWv-00027F-Jr for qemu-devel@nongnu.org; Thu, 03 Dec 2020 05:08:07 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606990084; 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=5sM8eYP2ae3GJXLwJ38CjqvOMa2DX4rJHQE2NkFSoaY=; b=N+WEKsQ5pCqdZ7czsaF7G+gw05HNzTNUFahxE9XVpFsDe0yQBn2nLY9jn7BTMKiuh0+8Ri rG5EBs/JWiEGdbMivEx6mLnLwjaFdgYL5N9u2GhnMms+QTpZwokEHwzlSj6fjhtfgx5sk7 GsKDOcEKmaIQVfsVBi+rUSeHBDF5xkc= 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-254-QPrXnorwNQGjBpSh2ovbUQ-1; Thu, 03 Dec 2020 05:08:02 -0500 X-MC-Unique: QPrXnorwNQGjBpSh2ovbUQ-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 74E99809DD4; Thu, 3 Dec 2020 10:08:01 +0000 (UTC) Received: from [10.36.113.250] (ovpn-113-250.ams2.redhat.com [10.36.113.250]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1827260C17; Thu, 3 Dec 2020 10:07:42 +0000 (UTC) Subject: Re: [PATCH v1 4/9] vfio: Support for RamDiscardMgr in the !vIOMMU case To: Alex Williamson References: <20201119153918.120976-1-david@redhat.com> <20201119153918.120976-5-david@redhat.com> <20201202162633.27cb15b6@w520.home> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Thu, 3 Dec 2020 11:07:42 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20201202162633.27cb15b6@w520.home> 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 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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: -35 X-Spam_score: -3.6 X-Spam_bar: --- X-Spam_report: (-3.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.495, 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_NONE=-0.0001, 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" , qemu-devel@nongnu.org, Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , teawater , Igor Mammedov , Paolo Bonzini , Luiz Capitulino , Marek Kedzierski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 03.12.20 00:26, Alex Williamson wrote: > On Thu, 19 Nov 2020 16:39:13 +0100 > David Hildenbrand wrote: > >> Implement support for RamDiscardMgr, to prepare for virtio-mem >> support. Instead of mapping the whole memory section, we only map >> "populated" parts and update the mapping when notified about >> discarding/population of memory via the RamDiscardListener. Similarly, when >> syncing the dirty bitmaps, sync only the actually mapped (populated) parts >> by replaying via the notifier. >> >> Small mapping granularity is problematic for vfio, because we might run out >> of mappings. Warn to at least make users aware that there is such a >> limitation and that we are dealing with a setup issue e.g., of >> virtio-mem devices. >> >> Using virtio-mem with vfio is still blocked via >> ram_block_discard_disable()/ram_block_discard_require() after this patch. >> >> Cc: Paolo Bonzini >> Cc: "Michael S. Tsirkin" >> Cc: Alex Williamson >> Cc: Dr. David Alan Gilbert >> Cc: Igor Mammedov >> Cc: Pankaj Gupta >> Cc: Peter Xu >> Cc: Auger Eric >> Cc: Wei Yang >> Cc: teawater >> Cc: Marek Kedzierski >> Signed-off-by: David Hildenbrand >> --- >> hw/vfio/common.c | 233 ++++++++++++++++++++++++++++++++++ >> include/hw/vfio/vfio-common.h | 12 ++ >> 2 files changed, 245 insertions(+) >> >> diff --git a/hw/vfio/common.c b/hw/vfio/common.c >> index c1fdbf17f2..d52e7356cb 100644 >> --- a/hw/vfio/common.c >> +++ b/hw/vfio/common.c > ... >> +static void vfio_register_ram_discard_notifier(VFIOContainer *container, >> + MemoryRegionSection *section) >> +{ >> + RamDiscardMgr *rdm = memory_region_get_ram_discard_mgr(section->mr); >> + RamDiscardMgrClass *rdmc = RAM_DISCARD_MGR_GET_CLASS(rdm); >> + MachineState *ms = MACHINE(qdev_get_machine()); >> + uint64_t suggested_granularity; >> + VFIORamDiscardListener *vrdl; >> + int ret; >> + >> + vrdl = g_new0(VFIORamDiscardListener, 1); >> + vrdl->container = container; >> + vrdl->mr = section->mr; >> + vrdl->offset_within_region = section->offset_within_region; >> + vrdl->offset_within_address_space = section->offset_within_address_space; >> + vrdl->size = int128_get64(section->size); >> + vrdl->granularity = rdmc->get_min_granularity(rdm, section->mr); >> + >> + /* Ignore some corner cases not relevant in practice. */ >> + g_assert(QEMU_IS_ALIGNED(vrdl->offset_within_region, TARGET_PAGE_SIZE)); >> + g_assert(QEMU_IS_ALIGNED(vrdl->offset_within_address_space, >> + TARGET_PAGE_SIZE)); >> + g_assert(QEMU_IS_ALIGNED(vrdl->size, TARGET_PAGE_SIZE)); >> + >> + /* >> + * We assume initial RAM never has a RamDiscardMgr and that all memory >> + * to eventually get hotplugged later could be coordinated via a >> + * RamDiscardMgr ("worst case"). >> + * >> + * We assume the Linux kernel is configured ("dma_entry_limit") for the >> + * maximum of 65535 mappings and that we can consume roughly half of that > > > s/maximum/default/ > > Deciding we should only use half of it seems arbitrary. Yeah, it's sub-optimal - bad heuristic :) . What would be your suggestion for a better heuristic? My gut feeling would be that we rarely use more than 512 mappings in the system address space (e.g., maximum number of DIMMs is 256). > > >> + * for this purpose. >> + * >> + * In reality, we might also have RAM without a RamDiscardMgr in our device >> + * memory region and might be able to consume more mappings. >> + */ >> + suggested_granularity = pow2ceil((ms->maxram_size - ms->ram_size) / 32768); >> + suggested_granularity = MAX(suggested_granularity, 1 * MiB); >> + if (vrdl->granularity < suggested_granularity) { >> + warn_report("%s: eventually problematic mapping granularity (%" PRId64 >> + " MiB) with coordinated discards (e.g., 'block-size' in" >> + " virtio-mem). Suggested minimum granularity: %" PRId64 >> + " MiB", __func__, vrdl->granularity / MiB, >> + suggested_granularity / MiB); >> + } > > > Starting w/ kernel 5.10 we have a way to get the instantaneous count of > available DMA mappings, so we could avoid assuming 64k when that's > available (see ex. s390_pci_update_dma_avail()). Interesting, I missed that interface. Will have a look. TThanks! -- Thanks, David / dhildenb