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=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 952C9C433DB for ; Tue, 5 Jan 2021 10:00:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44A6D22288 for ; Tue, 5 Jan 2021 10:00:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728291AbhAEKAS (ORCPT ); Tue, 5 Jan 2021 05:00:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:59666 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725919AbhAEKAS (ORCPT ); Tue, 5 Jan 2021 05:00:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1609840731; 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=2jEtueBz8ZOvS21YvDXkoHLYxQlQJlmCqkVMoZHehj0=; b=KuUkVBHISS+POQ5/+rUP1N4ryxGI9s4wqL3JMSLsSxJbgLc0QmlzqcaqRcwshOtwdCCLiA +wUb5G9sK+3wPgz2Uf5KjDGaX6umeYEVXQZZ3Wf70QHhM2dZ3RpK4Pv3VeYrauQVs8pVUa WSKZueLQoHqXE6ltjHardapZV8Ys/jg= 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-571-nLM0Vp2RMpScV7p3f5W1rA-1; Tue, 05 Jan 2021 04:58:49 -0500 X-MC-Unique: nLM0Vp2RMpScV7p3f5W1rA-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 7DA00800D55; Tue, 5 Jan 2021 09:58:48 +0000 (UTC) Received: from [10.36.114.117] (ovpn-114-117.ams2.redhat.com [10.36.114.117]) by smtp.corp.redhat.com (Postfix) with ESMTP id A3AFF60BE5; Tue, 5 Jan 2021 09:58:47 +0000 (UTC) Subject: Re: uninitialized pmem struct pages To: Dan Williams Cc: Michal Hocko , Linux MM , LKML References: <20210104100323.GC13207@dhcp22.suse.cz> <033e1cd6-9762-5de6-3e88-47d3038fda7f@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: Date: Tue, 5 Jan 2021 10:58:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.01.21 10:56, Dan Williams wrote: > On Tue, Jan 5, 2021 at 1:37 AM David Hildenbrand wrote: >> >>>> Yeah, obviously the first one. Being able to add+use PMEM is more >>>> important than using each and every last MB of main memory. >>>> >>>> I wonder if we can just stop adding any system RAM like >>>> >>>> [ Memory Section ] >>>> [ RAM ] [ Hole ] >>>> >>>> When there could be the possibility that the hole might actually be >>>> PMEM. (e.g., with CONFIG_ZONE_DEVICE and it being the last section in a >>>> sequence of sections, not just a tiny hole) >>> >>> I like the simplicity of it... I worry that the capacity loss >>> regression is easy to notice by looking at the output of free(1) from >>> one kernel to the next and someone screams. >> >> Well, you can always make it configurable and then simply fail to add >> PMEM later if impossible (trying to sub-section hot-add into early >> section). It's in the hands of the sysadmin then ("max out system ram" >> vs. "support any PMEM device that could eventually be there at >> runtime"). Distros would go for the second. >> >> I agree that it's not optimal, but sometimes simplicity has to win. > > Here's where we left it last time, open to pfn_to_online_page hacks... > > https://lore.kernel.org/linux-mm/CAPcyv4ivq=EPUePXiX2ErcVyF7+dV9Yv215Oue7X_Y2X_Jfw8Q@mail.gmail.com > Yeah, I recall. That's why I favor simple approaches right now - less brain power to waste ;) > I don't think a slow-path flag in the mem-section is too onerous, but > I'll withhold judgement until I have the patch I'm thinking of > in-hand. Let me give it a shot, you can always nack the final result. Sure! -- Thanks, David / dhildenb