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Wed, 08 Jun 2022 07:11:31 -0700 (PDT) Date: Wed, 8 Jun 2022 10:11:31 -0400 From: Johannes Weiner To: "Aneesh Kumar K.V" Cc: linux-mm@kvack.org, akpm@linux-foundation.org, Wei Xu , Huang Ying , Greg Thelen , Yang Shi , Davidlohr Bueso , Tim C Chen , Brice Goglin , Michal Hocko , Linux Kernel Mailing List , Hesham Almatary , Dave Hansen , Jonathan Cameron , Alistair Popple , Dan Williams , Feng Tang , Jagdish Gediya , Baolin Wang , David Rientjes Subject: Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers Message-ID: References: <20220603134237.131362-1-aneesh.kumar@linux.ibm.com> <20220603134237.131362-2-aneesh.kumar@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220603134237.131362-2-aneesh.kumar@linux.ibm.com> X-Stat-Signature: oh5m6etzgq3aup3j4atsedanwbxepgoq Authentication-Results: imf25.hostedemail.com; dkim=pass header.d=cmpxchg-org.20210112.gappssmtp.com header.s=20210112 header.b=xq48c4rS; dmarc=pass (policy=none) header.from=cmpxchg.org; spf=pass (imf25.hostedemail.com: domain of hannes@cmpxchg.org designates 209.85.160.173 as permitted sender) smtp.mailfrom=hannes@cmpxchg.org X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 13D9AA007D X-HE-Tag: 1654697492-718097 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: Hi Aneesh, On Fri, Jun 03, 2022 at 07:12:29PM +0530, Aneesh Kumar K.V wrote: > @@ -0,0 +1,20 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _LINUX_MEMORY_TIERS_H > +#define _LINUX_MEMORY_TIERS_H > + > +#ifdef CONFIG_TIERED_MEMORY > + > +#define MEMORY_TIER_HBM_GPU 0 > +#define MEMORY_TIER_DRAM 1 > +#define MEMORY_TIER_PMEM 2 > + > +#define MEMORY_RANK_HBM_GPU 300 > +#define MEMORY_RANK_DRAM 200 > +#define MEMORY_RANK_PMEM 100 > + > +#define DEFAULT_MEMORY_TIER MEMORY_TIER_DRAM > +#define MAX_MEMORY_TIERS 3 I understand the names are somewhat arbitrary, and the tier ID space can be expanded down the line by bumping MAX_MEMORY_TIERS. But starting out with a packed ID space can get quite awkward for users when new tiers - especially intermediate tiers - show up in existing configurations. I mentioned in the other email that DRAM != DRAM, so new tiers seem inevitable already. It could make sense to start with a bigger address space and spread out the list of kernel default tiers a bit within it: MEMORY_TIER_GPU 0 MEMORY_TIER_DRAM 10 MEMORY_TIER_PMEM 20 etc.