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=-7.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 2091EC4338F for ; Mon, 23 Aug 2021 10:35:08 +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 6E6AC6137B for ; Mon, 23 Aug 2021 10:35:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6E6AC6137B 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]:37912 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mI7II-0007P4-6Z for qemu-devel@archiver.kernel.org; Mon, 23 Aug 2021 06:35:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:52078) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mI7HT-00061r-KV for qemu-devel@nongnu.org; Mon, 23 Aug 2021 06:34:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:52527) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mI7HQ-0004bL-4J for qemu-devel@nongnu.org; Mon, 23 Aug 2021 06:34:14 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629714850; 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=HgDlsPR7E6wDSuQkKvJtqiANX5xHQaG9OKseRImxNg8=; b=TkVvmmnUFteSVD0FPIR7V2Gml+Eqqo1PuHoHIP9HSDnOYVraxGNZcyCpQa8SHKAf0KU6PP 5C+T6zxLxjRviSfVD5qX1C2HV+Kcv45MWuHX+nob4SSSQ9xdLZJHIdgLSR13i71dxnXj0k NdwdIWZpyTio6KbRm6Oqz3AIKNbm2FE= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-490-tMQUMvrqOuiz3ieB6WKAQQ-1; Mon, 23 Aug 2021 06:34:08 -0400 X-MC-Unique: tMQUMvrqOuiz3ieB6WKAQQ-1 Received: by mail-wm1-f69.google.com with SMTP id b3-20020a1c80030000b02902e6a7296cb3so2827749wmd.5 for ; Mon, 23 Aug 2021 03:34:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=HgDlsPR7E6wDSuQkKvJtqiANX5xHQaG9OKseRImxNg8=; b=rZwAiDYvnZZk+3Yt1g17CdZdWBppfepxzQdrhCD0+/Beq/JMYUsPsjGEflml1+/qXx BrD1aupwkkUb7B3Nu0Qj35vloxtNLYC/EEvbxajvY9RR/kCZcmXN+KAOOaEEVb9VrIC3 Ju5eZpzq/6hldjDq5eonVTVTY0fOhDKB7jFW6xF+RvY1PCiq4vVRMWyEh0OLiyus/dVB fBjW2SjvVAGJ2U7px4wwyUFR6RtqbpQheyC7MwXvvHedOkT2dfyo/tx3uKMAoll6/iKK edWAftAPpNEe90Y1IcAlS2RrEAii8l+JYA2NgRgTnQd9yarIIwBCVsUXWUStz9W6TTEJ IeBw== X-Gm-Message-State: AOAM533ALX7hBP27AWr+k2dKiENFrb7JIYENOtAAqFVWvFabWb5qOJm3 G1vT8gqqQBfTAxeFjyeWaqjpjH+n3S/bBZo9uhe5eexjnONa/tUTH9Oq6mB3Z33NiPSuIv3VQ+Y +pxzliJTkUhX0cmE= X-Received: by 2002:adf:d4ce:: with SMTP id w14mr12860936wrk.407.1629714847795; Mon, 23 Aug 2021 03:34:07 -0700 (PDT) X-Google-Smtp-Source: ABdhPJx/LfjEw5eeeC4Izq+sD4++17/XIo3HqZe/xesJ+ByBcFxKit86oWoqd8IxFWIsS6GkqA5HkA== X-Received: by 2002:adf:d4ce:: with SMTP id w14mr12860915wrk.407.1629714847585; Mon, 23 Aug 2021 03:34:07 -0700 (PDT) Received: from [192.168.1.36] (163.red-83-52-55.dynamicip.rima-tde.net. [83.52.55.163]) by smtp.gmail.com with ESMTPSA id k17sm18218481wmj.0.2021.08.23.03.34.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Aug 2021 03:34:07 -0700 (PDT) Subject: Re: [PATCH] softmmu/physmem: Improve guest memory allocation failure error message To: David Hildenbrand , Peter Maydell References: <20210820155211.3153137-1-philmd@redhat.com> <20a53e29-ba23-fe0d-f961-63d0b5ca9a89@redhat.com> <6165f86e-1ce7-d178-1f5c-4b3c5110f0c1@redhat.com> <1a63c2d2-7420-5fc1-1023-0504a67dc40b@redhat.com> <628a7ee5-b88d-c043-2e67-67e791532c18@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 23 Aug 2021 12:34:06 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <628a7ee5-b88d-c043-2e67-67e791532c18@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@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: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -44 X-Spam_score: -4.5 X-Spam_bar: ---- X-Spam_report: (-4.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.746, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.959, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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: QEMU Developers , Peter Xu , "Dr. David Alan Gilbert" , Paolo Bonzini , Igor Mammedov , Bin Meng Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/23/21 12:24 PM, David Hildenbrand wrote: > On 23.08.21 12:12, Philippe Mathieu-Daudé wrote: >> On 8/23/21 11:29 AM, David Hildenbrand wrote: >>> On 23.08.21 11:23, Peter Maydell wrote: >>>> On Mon, 23 Aug 2021 at 09:40, David Hildenbrand >>>> wrote: >>>>> Not opposed to printing the size, although I doubt that it will really >>>>> stop similar questions/problems getting raised. >>>> >>>> The case that triggered this was somebody thinking >>>> -m took a byte count, so very likely that an error message >>>> saying "you tried to allocate 38TB" would have made their >>>> mistake clear in a way that just "allocation failed" did not. >>>> It also means that if a future user asks us for help then >>>> we can look at the error message and immediately tell them >>>> the problem, rather than going "hmm, what are all the possible >>>> ways that allocation might have failed" and going off down >>>> rabbitholes like VM overcommit settings... >>> >>> We've had similar issues recently where Linux memory overcommit handling >>> rejected the allocation -- and the user was well aware about the actual >>> size. You won't be able to catch such reports, because people don't >>> understand how Linux memory overcommit handling works or was configured. >>> >>> "I have 3 GiB of free memory, why can't I create a 3 GiB VM". "I have 3 >>> GiB of RAM, why can't I create a 3 GiB VM even if it won't make use of >>> all 3 GiB of memory". >>> >>> Thus my comment, it will only stop very basic usage issues. And I agree >>> that looking at the error *might* help. It didn't help for the cases I >>> just described, because we need much more system information to make a >>> guess what the user error actually is. >> >> Is it possible to get the maximal overcommitable amount on Linux? > > Not reliably I think. > > In the "always" mode, there is none. > > In the "guess"/"estimate" mode, the kernel takes a guess (currently > implemented as checking if the mmap size <= total RAM + total SWAP). >     Committable = MemTotal + SwapTotal > > In the "never" mode: >     Committable = CommitLimit - Committed_AS > However, the value gets further reduced for !root applications by > /proc/sys/vm/admin_reserve_kbytes. > > Replicating these calculations in user space would be suboptimal IMHO. What about simply giving a hint about memory overcommit and display a link to documentation with longer description about how to check and figure out this issue?