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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 60E62C433E0 for ; Mon, 15 Mar 2021 17:26:57 +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 10D1864EB3 for ; Mon, 15 Mar 2021 17:26:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10D1864EB3 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]:42724 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lLqzX-0001qk-W0 for qemu-devel@archiver.kernel.org; Mon, 15 Mar 2021 13:26:56 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43910) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lLqio-0004kY-H4 for qemu-devel@nongnu.org; Mon, 15 Mar 2021 13:09:41 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:52890) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lLqim-00034i-7n for qemu-devel@nongnu.org; Mon, 15 Mar 2021 13:09:37 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615828174; h=from:from:reply-to: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=rumidTToSKGbj23cDwM0aiSnJMQtpDSGBxd20cVFr+Q=; b=F8VTs9+H3prXT+WEe+GH3sP0G4li0WmPwhSQ7aXK4PqjzKbnFQ/QYTIU8/c5nOWNtkaNeM GokOdAa4xLLVn15Yg8qxubmHUy6WRCfpYHj8cHgDmnOBn2E1kS5TSxvHe70Or+QQZS922C ptj61OzM09dFn7zTIrQVG/6iUE2caVY= 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-398-9xDiEB-6Oh2Uucq3oi1ILw-1; Mon, 15 Mar 2021 13:09:21 -0400 X-MC-Unique: 9xDiEB-6Oh2Uucq3oi1ILw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6735918460E1; Mon, 15 Mar 2021 17:09:20 +0000 (UTC) Received: from redhat.com (ovpn-115-81.ams2.redhat.com [10.36.115.81]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F2EF55D9C0; Mon, 15 Mar 2021 17:09:15 +0000 (UTC) Date: Mon, 15 Mar 2021 17:09:13 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Thomas Huth Subject: Re: [RFC PATCH] docs/devel: expand style section of memory management Message-ID: References: <20210315165312.22453-1-alex.bennee@linaro.org> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=berrange@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, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , Alex =?utf-8?Q?Benn=C3=A9e?= , QEMU Developers , Stefan Hajnoczi Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Mar 15, 2021 at 06:04:10PM +0100, Thomas Huth wrote: > 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. On a Linux host you're almost certainly not going to see g_malloc fail for small allocations at least. Instead at some point the host will be under enough memory pressure that the OOM killer activates and reaps arbitrary processes based on some criteria it has, freeing up memory for malloc to succeed (unless OOM killer picked you as the victim). Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|