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Wed, 8 Jun 2022 04:58:51 GMT Received: from d06av21.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6979E52050; Wed, 8 Jun 2022 04:58:49 +0000 (GMT) Received: from [9.43.53.124] (unknown [9.43.53.124]) by d06av21.portsmouth.uk.ibm.com (Postfix) with ESMTP id B80465204F; Wed, 8 Jun 2022 04:58:43 +0000 (GMT) Message-ID: <2b4f053b-de25-986c-f764-5cc6a28f4953@linux.ibm.com> Date: Wed, 8 Jun 2022 10:28:42 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.10.0 Subject: Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers Content-Language: en-US To: Yang Shi Cc: Linux MM , Andrew Morton , Wei Xu , Huang Ying , Greg Thelen , 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 References: <20220603134237.131362-1-aneesh.kumar@linux.ibm.com> <20220603134237.131362-2-aneesh.kumar@linux.ibm.com> From: Aneesh Kumar K V In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed X-TM-AS-GCONF: 00 X-Proofpoint-GUID: mqFmMGm7_hI-s72ja6qqoNLUbPkdf9jb X-Proofpoint-ORIG-GUID: AnRpjh8OxVwHUdgpyFAbfDTevpU3deF5 Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.517,FMLib:17.11.64.514 definitions=2022-06-08_01,2022-06-07_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 clxscore=1015 impostorscore=0 spamscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 mlxscore=0 mlxlogscore=915 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2204290000 definitions=main-2206080019 X-Rspamd-Queue-Id: 475C5180054 X-Stat-Signature: ccahspiqs55ojtrz8c738oo8azeshna9 X-Rspam-User: Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=ibm.com header.s=pp1 header.b=LP7ztqz5; spf=pass (imf06.hostedemail.com: domain of aneesh.kumar@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=aneesh.kumar@linux.ibm.com; dmarc=pass (policy=none) header.from=ibm.com X-Rspamd-Server: rspam08 X-HE-Tag: 1654664470-517921 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: On 6/8/22 3:02 AM, Yang Shi wrote: > On Fri, Jun 3, 2022 at 6:43 AM Aneesh Kumar K.V > wrote: >> >> In the current kernel, memory tiers are defined implicitly via a >> demotion path relationship between NUMA nodes, which is created >> during the kernel initialization and updated when a NUMA node is >> hot-added or hot-removed. The current implementation puts all >> nodes with CPU into the top tier, and builds the tier hierarchy >> tier-by-tier by establishing the per-node demotion targets based >> on the distances between nodes. >> >> This current memory tier kernel interface needs to be improved for >> several important use cases, >> >> The current tier initialization code always initializes >> each memory-only NUMA node into a lower tier. But a memory-only >> NUMA node may have a high performance memory device (e.g. a DRAM >> device attached via CXL.mem or a DRAM-backed memory-only node on >> a virtual machine) and should be put into a higher tier. >> >> The current tier hierarchy always puts CPU nodes into the top >> tier. But on a system with HBM or GPU devices, the >> memory-only NUMA nodes mapping these devices should be in the >> top tier, and DRAM nodes with CPUs are better to be placed into the >> next lower tier. >> >> With current kernel higher tier node can only be demoted to selected nodes on the >> next lower tier as defined by the demotion path, not any other >> node from any lower tier. This strict, hard-coded demotion order >> does not work in all use cases (e.g. some use cases may want to >> allow cross-socket demotion to another node in the same demotion >> tier as a fallback when the preferred demotion node is out of >> space), This demotion order is also inconsistent with the page >> allocation fallback order when all the nodes in a higher tier are >> out of space: The page allocation can fall back to any node from >> any lower tier, whereas the demotion order doesn't allow that. >> >> The current kernel also don't provide any interfaces for the >> userspace to learn about the memory tier hierarchy in order to >> optimize its memory allocations. >> >> This patch series address the above by defining memory tiers explicitly. >> >> This patch introduce explicity memory tiers with ranks. The rank >> value of a memory tier is used to derive the demotion order between >> NUMA nodes. The memory tiers present in a system can be found at >> >> /sys/devices/system/memtier/memtierN/ >> >> The nodes which are part of a specific memory tier can be listed >> via >> /sys/devices/system/memtier/memtierN/nodelist >> >> "Rank" is an opaque value. Its absolute value doesn't have any >> special meaning. But the rank values of different memtiers can be >> compared with each other to determine the memory tier order. >> >> For example, if we have 3 memtiers: memtier0, memtier1, memiter2, and >> their rank values are 300, 200, 100, then the memory tier order is: >> memtier0 -> memtier2 -> memtier1, where memtier0 is the highest tier >> and memtier1 is the lowest tier. >> >> The rank value of each memtier should be unique. >> >> A higher rank memory tier will appear first in the demotion order >> than a lower rank memory tier. ie. while reclaim we choose a node >> in higher rank memory tier to demote pages to as compared to a node >> in a lower rank memory tier. >> >> For now we are not adding the dynamic number of memory tiers. >> But a future series supporting that is possible. Currently >> number of tiers supported is limitted to MAX_MEMORY_TIERS(3). >> When doing memory hotplug, if not added to a memory tier, the NUMA >> node gets added to DEFAULT_MEMORY_TIER(1). >> >> This patch is based on the proposal sent by Wei Xu at [1]. >> >> [1] https://lore.kernel.org/linux-mm/CAAPL-u9Wv+nH1VOZTj=9p9S70Y3Qz3+63EkqncRDdHfubsrjfw@mail.gmail.com >> >> Suggested-by: Wei Xu >> Signed-off-by: Jagdish Gediya >> Signed-off-by: Aneesh Kumar K.V >> --- >> include/linux/memory-tiers.h | 20 ++++ >> mm/Kconfig | 11 ++ >> mm/Makefile | 1 + >> mm/memory-tiers.c | 188 +++++++++++++++++++++++++++++++++++ >> 4 files changed, 220 insertions(+) >> create mode 100644 include/linux/memory-tiers.h >> create mode 100644 mm/memory-tiers.c >> >> diff --git a/include/linux/memory-tiers.h b/include/linux/memory-tiers.h >> new file mode 100644 >> index 000000000000..e17f6b4ee177 >> --- /dev/null >> +++ b/include/linux/memory-tiers.h >> @@ -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 >> + >> +#endif /* CONFIG_TIERED_MEMORY */ >> + >> +#endif >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 169e64192e48..08a3d330740b 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -614,6 +614,17 @@ config ARCH_ENABLE_HUGEPAGE_MIGRATION >> config ARCH_ENABLE_THP_MIGRATION >> bool >> >> +config TIERED_MEMORY >> + bool "Support for explicit memory tiers" >> + def_bool n >> + depends on MIGRATION && NUMA >> + help >> + Support to split nodes into memory tiers explicitly and >> + to demote pages on reclaim to lower tiers. This option >> + also exposes sysfs interface to read nodes available in >> + specific tier and to move specific node among different >> + possible tiers. > > IMHO we should not need a new kernel config. If tiering is not present > then there is just one tier on the system. And tiering is a kind of > hardware configuration, the information could be shown regardless of > whether demotion/promotion is supported/enabled or not. > This was added so that we could avoid doing multiple #if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA) Initially I had that as def_bool y and depends on MIGRATION && NUMA. But it was later suggested that def_bool is not recommended for newer config. How about config TIERED_MEMORY bool "Support for explicit memory tiers" - def_bool n - depends on MIGRATION && NUMA - help - Support to split nodes into memory tiers explicitly and - to demote pages on reclaim to lower tiers. This option - also exposes sysfs interface to read nodes available in - specific tier and to move specific node among different - possible tiers. + def_bool MIGRATION && NUMA config HUGETLB_PAGE_SIZE_VARIABLE def_bool n ie, we just make it a Kconfig variable without exposing it to the user? -aneesh