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bh=996m6VksQ1/RmEaCfF7b9eJa5BsDq/DzM1GoSO+OXZA=; b=nAHmiLmTQczrQWdDzaHxioEnVjob7Yn6quiIzUI+b47qERvBC2XtQj4xG7c9mHsUwEps2+ 1E/IXztBJ8o323JLT+FnvGm+nLzwlEovS+AbdozraY/kIlpYLHVNiezj2T7b0rqT46/R9w +VgnwILrJ0+8YnLaeD2p6YXXW4RRQtU= Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 1F124136CF; Tue, 5 Dec 2023 09:09:17 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id mcboBb3obmX9SQAAD6G6ig (envelope-from ); Tue, 05 Dec 2023 09:09:17 +0000 Date: Tue, 5 Dec 2023 10:09:16 +0100 From: Michal Hocko To: Srinivasulu Thanneeru Cc: aneesh.kumar@linux.ibm.com, linux-cxl@vger.kernel.org, linux-mm@kvack.org, dan.j.williams@intel.com, hannes@cmpxchg.org, hasanalmaruf@fb.com, haowang3@fb.com, ying.huang@intel.com, gregory.price@memverge.com, tj@kernel.org, hezhongkun.hzk@bytedance.com, fvdl@google.com, john@jagalactic.com, emirakhur@micron.com, vtavarespetr@micron.com, Ravis.OpenSrc@micron.com, Jonathan.Cameron@huawei.com, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [EXT] Re: [RFC PATCH 0/2] Node migration between memory tiers Message-ID: References: <20231130220422.2033-1-sthanneeru.opensrc@micron.com> <1db561a9-6984-418d-9305-a2a5ece93696@micron.com> <2552828e-6865-4fa8-a9c4-8ed76dd85257@micron.com> <8eae7d95-fc98-4ac7-8f83-d0caee00bc87@micron.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8eae7d95-fc98-4ac7-8f83-d0caee00bc87@micron.com> X-Rspamd-Queue-Id: 178A5A0016 X-Rspam-User: X-Stat-Signature: c6pskirut5s51zebo14shn8mxg5dfaew X-Rspamd-Server: rspam01 X-HE-Tag: 1701767358-741196 X-HE-Meta: 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 jrbrdySu 9XpoWq1CvM2mNnk6ir1rng8nz9KtEOzZXPtXOQrKhwVEoY11JNRS4Mrg54Ydd70j1fbdRvY3q1g9RrYLWT4QJ1IYqMIpoqhaPPgUwmTCopcWnIpZi6/r1PP5QXm14KrGi0anEO/f2dweMV23KnM8bAee9esBVmWKA7yQ09CAUYhru6/0GNCkvTQ94eFG8js1bxtN6ZUy9gtSqA/XFjT7CHHvHIdcBCnWUmQ9KKlv5m6HycfaVzTvI8n9G+m3NvN8wOpkqhMtviw+cjxvyo2GOzdJPCg== 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: List-Subscribe: List-Unsubscribe: On Tue 05-12-23 14:32:20, Srinivasulu Thanneeru wrote: > > > On 12/5/2023 2:21 PM, Michal Hocko wrote: > > CAUTION: EXTERNAL EMAIL. Do not click links or open attachments unless you recognize the sender and were expecting this message. > > > > > > On Tue 05-12-23 14:12:17, Srinivasulu Thanneeru wrote: > > > > > > > > > On 12/5/2023 2:05 PM, Michal Hocko wrote: > > > > CAUTION: EXTERNAL EMAIL. Do not click links or open attachments unless you recognize the sender and were expecting this message. > > > > > > > > > > > > On Tue 05-12-23 01:26:07, Srinivasulu Thanneeru wrote: > > > > > > > > > > > > > > > On 12/4/2023 9:13 PM, Michal Hocko wrote: > > > > > > CAUTION: EXTERNAL EMAIL. Do not click links or open attachments unless you recognize the sender and were expecting this message. > > > > > > > > > > > > > > > > > > On Fri 01-12-23 03:34:20, sthanneeru.opensrc@micron.com wrote: > > > > > > > From: Srinivasulu Thanneeru > > > > > > > > > > > > > > The memory tiers feature allows nodes with similar memory types > > > > > > > or performance characteristics to be grouped together in a > > > > > > > memory tier. However, there is currently no provision for > > > > > > > moving a node from one tier to another on demand. > > > > > > > > > > > > Could you expand on why this is really needed/necessary? What is the > > > > > > actual usecase? > > > > > > > > > > Hi Michal Hock, > > > > > > > > > > Following two use-cases we have observed. > > > > > 1. It is not accurate to group similar memory types in the same tier, > > > > > because even similar memory types may have different speed grades. > > > > > > > > Presumably they are grouped based on a HW configuration. Does that mean > > > > that the configuration is wrong? Are you trying to workaround that by > > > > this interface? > > > > > > > > > 2. Some systems boots up with CXL devices and DRAM on the same memory-tier, > > > > > we need a way to move the CXL nodes to the correct tier from the user space. > > > > > > > > Again, could you expand a bit more and explain why this cannot be > > > > configured automatically? > > > > > > Yes, in both cases above, if hardware not automatically populated properly, > > > in that case this interface would help to correct it from user space. > > > > > > We had observed case-2 in our setups. > > > > How hard it is to address this at the HW level? > > > > Btw. this is really important piece of context that should be part of > > the changelog. Quite honestly introducing user interfaces solely to > > workaround HW issues seems a rather weak justification. Are there any > > usecases you can think of where this would be useful? > > I'm not sure how difficult to fix it in the hardware. Please explore that. It is sad to see learn that CXL which is a really new technology is already fighting with misconfigurations. -- Michal Hocko SUSE Labs