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=-5.3 required=3.0 tests=BAYES_00, 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 02281C4338F for ; Tue, 10 Aug 2021 19:23:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CBB9060F41 for ; Tue, 10 Aug 2021 19:23:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232452AbhHJTYO (ORCPT ); Tue, 10 Aug 2021 15:24:14 -0400 Received: from mga09.intel.com ([134.134.136.24]:48238 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231152AbhHJTYN (ORCPT ); Tue, 10 Aug 2021 15:24:13 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10072"; a="214962085" X-IronPort-AV: E=Sophos;i="5.84,310,1620716400"; d="scan'208";a="214962085" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Aug 2021 12:23:51 -0700 X-IronPort-AV: E=Sophos;i="5.84,310,1620716400"; d="scan'208";a="515958752" Received: from akleen-mobl1.amr.corp.intel.com (HELO [10.209.69.62]) ([10.209.69.62]) by fmsmga003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Aug 2021 12:23:49 -0700 Subject: Re: [PATCH 1/5] mm: Add support for unaccepted memory To: Dave Hansen , "Kirill A. Shutemov" , Borislav Petkov , Andy Lutomirski , Sean Christopherson , Andrew Morton , Joerg Roedel Cc: Kuppuswamy Sathyanarayanan , David Rientjes , Vlastimil Babka , Tom Lendacky , Thomas Gleixner , Peter Zijlstra , Paolo Bonzini , Ingo Molnar , Varad Gautam , Dario Faggioli , x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" References: <20210810062626.1012-1-kirill.shutemov@linux.intel.com> <20210810062626.1012-2-kirill.shutemov@linux.intel.com> <9748c07c-4e59-89d0-f425-c57f778d1b42@linux.intel.com> <17b6a3a3-bd7d-f57e-8762-96258b16247a@intel.com> From: Andi Kleen Message-ID: <796a4b20-7fa3-3086-efa0-2f728f35ae06@linux.intel.com> Date: Tue, 10 Aug 2021 12:23:48 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <17b6a3a3-bd7d-f57e-8762-96258b16247a@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > But, not everyone is going to agree with me. Both the Intel TDX and the AMD SEV side independently came to opposite conclusions. In general people care a lot about boot time of VM guests. > > This also begs the question of how folks know when this "blip" is over. > Do we have a counter for offline pages? Is there any way to force page > acceptance? Or, are we just stuck allocating a bunch of memory to warm > up the system? > > How do folks who care about these new blips avoid them? It's not different than any other warmup. At warmup time you always have lots of blips until the working set stabilizes. For example in virtualization first touch of a new page is usually an EPT violation handled to the host. Or in the native case you may need to do IO or free memory. Everybody who based their critical latency percentiles around a warming up process would be foolish, the picture would be completely distorted. So the basic operation is adding some overhead, but I don't think anything is that unusual compared to the state of the art. Now perhaps the locking might be a problem if the other operations all run in parallel, causing unnecessary serialization If that's really a problem I guess we can optimize later. I don't think there's anything fundamental about the current locking. -Andi