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[2620:137:e000::1:20]) by mx.google.com with ESMTP id s1-20020a056402520100b00461bbc0f917si2785960edd.605.2022.10.25.03.47.10; Tue, 25 Oct 2022 03:47:36 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@alien8.de header.s=dkim header.b=P0z3I0xw; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=alien8.de Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231494AbiJYKcD (ORCPT + 99 others); Tue, 25 Oct 2022 06:32:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231375AbiJYKcB (ORCPT ); Tue, 25 Oct 2022 06:32:01 -0400 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAC42D8ED3 for ; Tue, 25 Oct 2022 03:32:00 -0700 (PDT) Received: from zn.tnic (p200300ea9733e753329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ea:9733:e753:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 594351EC04CB; Tue, 25 Oct 2022 12:31:59 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1666693919; 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:in-reply-to:in-reply-to: references:references; bh=ai++jgLmenhahiBLse1vLJYEB/bd3+G6lQ4acR+CSyY=; b=P0z3I0xwj2YyygD/nk8kPmHQz8xOPhwrirQ4FKwWdW+LYy3NzSZiRAcnVsDad4/4TyA+Id C+dIkSRTyCBWdW6AUgSdcRLJzREMPfzuSdYMC78Rx5/r6BqAXRtj4u1KDAn+pdlC6xIfU4 MRXEub1PBMS0Jdrf8LEWllVjz5u5FYg= Date: Tue, 25 Oct 2022 12:31:59 +0200 From: Borislav Petkov To: Baoquan He Cc: Eric DeVolder , Oscar Salvador , Andrew Morton , david@redhat.com, linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, sourabhjain@linux.ibm.com, linux-mm@kvack.org Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support Message-ID: References: <53aed03e-2eed-09b1-9532-fe4e497ea47d@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 13, 2022 at 10:57:28AM +0800, Baoquan He wrote: > The concern to range number mainly is on Virt guest systems. And why would virt emulate 1K hotpluggable DIMM slots and not emulate a real machine? > On baremetal system, basically only very high end server support > memory hotplug. I ever visited customer's lab and saw one server, > it owns 8 slots, on each slot a box containing about 20 cpus and 2T > memory at most can be plugged in at one time. So people won't make too > many slots for hotplugging since it's too expensive. There you have it - the persuading argument. > I checked user space kexec code, the maximum memory range number is > honored to x86_64 because of a HPE SGI system. After that, nobody > complains about it. Please see below user space kexec-tools commit in > https://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git > > The memory ranges may be not all made by different DIMM slots, could be > firmware reservatoin, e.g efi/BIOS diggged out physical memory, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ I don't know what that means. If it is firmware crap, you want to exclude that from kdump anyway. > Now CONFIG_NR_CPUS has the maximum number as 8192. And user space > kexec-tools has maximum memory range number as 2048. We can take > the current 8192 + 2048 = 10K as default value conservatively. Or > take 8192 + 2048 * 2 = 12K which has two times of maximum memory range > bumber in kexec-tools. What do you think? I still think that we should stick to reality and support what is possible not what is potentially and theoretically there. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette