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=-5.1 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 A6788C433E0 for ; Mon, 15 Mar 2021 17:12:47 +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 57388600CD for ; Mon, 15 Mar 2021 17:12:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 57388600CD 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]:46576 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lLqlq-0006ye-Cm for qemu-devel@archiver.kernel.org; Mon, 15 Mar 2021 13:12:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42344) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lLqdr-0000wn-HP for qemu-devel@nongnu.org; Mon, 15 Mar 2021 13:04:32 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:33628) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lLqdk-0001Bq-2g for qemu-devel@nongnu.org; Mon, 15 Mar 2021 13:04:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615827861; 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=C6BnTicX3shKAD1S3WXlgvS0GO9KfJKX+30P+He8BGc=; b=WVENnsrjM2cmaS59O5u4vZ6E5UWfSTBfY/OqYOVN9YELH8z26UgtDjZPGIsjfwzQGmCoeL wZ7V6tCei7BPkAaeMkqzSYuAXmVEogxELpBoMsw6QQBU8WDIlor4/DuVrHYw2jOtB9CdIK 78g2DB+oZiQLbhKc4+UOi9TZSRXtYf0= 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-265-8aXJYMGUMGCyvm9QgRniGQ-1; Mon, 15 Mar 2021 13:04:16 -0400 X-MC-Unique: 8aXJYMGUMGCyvm9QgRniGQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9975EEC1A0; Mon, 15 Mar 2021 17:04:15 +0000 (UTC) Received: from thuth.remote.csb (ovpn-112-72.ams2.redhat.com [10.36.112.72]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5253E59461; Mon, 15 Mar 2021 17:04:10 +0000 (UTC) Subject: Re: [RFC PATCH] docs/devel: expand style section of memory management To: Peter Maydell , =?UTF-8?Q?Alex_Benn=c3=a9e?= References: <20210315165312.22453-1-alex.bennee@linaro.org> From: Thomas Huth Message-ID: Date: Mon, 15 Mar 2021 18:04:10 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=thuth@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=216.205.24.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.25, 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_H3=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: "Daniel P. Berrange" , QEMU Developers , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 15/03/2021 17.57, Peter Maydell wrote: > On Mon, 15 Mar 2021 at 16:53, Alex Bennée wrote: >> -Prefer g_new(T, n) instead of g_malloc(sizeof(T) ``*`` n) for the following >> +Care should be taken to avoid introducing places where the guest could >> +trigger an exit. For example using ``g_malloc`` on start-up is fine >> +if the result of a failure is going to be a fatal exit anyway. There >> +may be some start-up cases where failing is unreasonable (for example >> +speculatively loading debug symbols). >> + >> +However if we are doing an allocation because of something the guest >> +has done we should never trigger an exit. The code may deal with this >> +by trying to allocate less memory and continue or re-designed to allocate >> +buffers on start-up. > > I think this is overly strong. We want to avoid malloc-or-die for > cases where the guest gets to decide how big the allocation is; > but if we're doing a single small fixed-size allocation that happens > to be triggered by a guest action we should be OK to g_malloc() that > I think. I agree with Peter. If the host is so much out-of-memory that we even can't allocate some few bytes anymore (let's say less than 4k), the system is pretty much dead anyway and it might be better to terminate the program immediately instead of continuing with the out-of-memory situation. Thomas