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 B4797C433E0 for ; Tue, 5 Jan 2021 09:58:54 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 3736622288 for ; Tue, 5 Jan 2021 09:58:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3736622288 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 6E2B38D007B; Tue, 5 Jan 2021 04:58:53 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 691E28D006E; Tue, 5 Jan 2021 04:58:53 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5A78F8D007B; Tue, 5 Jan 2021 04:58:53 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0160.hostedemail.com [216.40.44.160]) by kanga.kvack.org (Postfix) with ESMTP id 47B188D006E for ; Tue, 5 Jan 2021 04:58:53 -0500 (EST) Received: from smtpin22.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 0A262EFDD for ; Tue, 5 Jan 2021 09:58:53 +0000 (UTC) X-FDA: 77671272546.22.cork10_1a0a62f274d8 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin22.hostedemail.com (Postfix) with ESMTP id E344418038E60 for ; Tue, 5 Jan 2021 09:58:52 +0000 (UTC) X-HE-Tag: cork10_1a0a62f274d8 X-Filterd-Recvd-Size: 4424 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf21.hostedemail.com (Postfix) with ESMTP for ; Tue, 5 Jan 2021 09:58:52 +0000 (UTC) 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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