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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C620C761AF for ; Fri, 31 Mar 2023 13:42:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232496AbjCaNmq (ORCPT ); Fri, 31 Mar 2023 09:42:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229894AbjCaNmn (ORCPT ); Fri, 31 Mar 2023 09:42:43 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 773E9B459; Fri, 31 Mar 2023 06:42:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=5I4KJmBZJA/j7wJDLeyLVxjH0xULgErbT1T9v7RMqcs=; b=J/R1MzB9Wucb7Y6h+C/8TofVal hbhTT7g+hEVNm07PTNpHSf2Du4f34BaxCv43dkaCIAFZNVLIAdvUgF+Lqcb9h/MwsXqmTMWnZyJgM nDrGhAf8V4j8Np89cjjY8HFZxl8gSOL1hTkM4SH5yItR6AaN+g+O09BX+TUxpGjKY920nIXIuCe0m SZRbZcHvbXlGqyhMcCA6uQ7a/95YZq1h/Mo7eLK2W3h4SkQM/4ppupkR59gw5PkRaqluZun0O3eBn jAyDFK9BTcd2lY6+YqDbpuC+u+XBpI+2GCLkpoWg67lhHKo3hh7glr7YiRNqXMDJv6OBBtCzhwkBo i7Sk8wIQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1piF1S-00BSqh-9A; Fri, 31 Mar 2023 13:42:30 +0000 Date: Fri, 31 Mar 2023 14:42:30 +0100 From: Matthew Wilcox To: Kyungsan Kim Cc: david@redhat.com, lsf-pc@lists.linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-cxl@vger.kernel.org, a.manzanares@samsung.com, viacheslav.dubeyko@bytedance.com, dan.j.williams@intel.com, seungjun.ha@samsung.com, wj28.lee@samsung.com Subject: Re: RE: FW: [LSF/MM/BPF TOPIC] SMDK inspired MM changes for CXL Message-ID: References: <7c7933df-43da-24e3-2144-0551cde05dcd@redhat.com> <20230331114220.400297-1-ks0204.kim@samsung.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230331114220.400297-1-ks0204.kim@samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-cxl@vger.kernel.org On Fri, Mar 31, 2023 at 08:42:20PM +0900, Kyungsan Kim wrote: > Given our experiences/design and industry's viewpoints/inquiries, > I will prepare a few slides in the session to explain > 1. Usecase - user/kernespace memory tiering for near/far placement, memory virtualization between hypervisor/baremetal OS > 2. Issue - movability(movable/unmovable), allocation(explicit/implicit), migration(intented/unintended) > 3. HW - topology(direct, switch, fabric), feature(pluggability,error-handling,etc) I think you'll find everybody else in the room understands these issues rather better than you do. This is hardly the first time that we've talked about CXL, and CXL is not the first time that people have proposed disaggregated memory, nor heterogenous latency/bandwidth systems. All the previous attempts have failed, and I expect this one to fail too. Maybe there's something novel that means this time it really will work, so any slides you do should focus on that. A more profitable discussion might be: 1. Should we have the page allocator return pages from CXL or should CXL memory be allocated another way? 2. Should there be a way for userspace to indicate that it prefers CXL memory when it calls mmap(), or should it always be at the discretion of the kernel? 3. Do we continue with the current ZONE_DEVICE model, or do we come up with something new?