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Mon, 11 Jul 2022 15:29:56 GMT Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 07623C6055; Mon, 11 Jul 2022 15:29:56 +0000 (GMT) Received: from b03ledav006.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EA8DEC605A; Mon, 11 Jul 2022 15:29:49 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.43.72.14]) by b03ledav006.gho.boulder.ibm.com (Postfix) with ESMTP; Mon, 11 Jul 2022 15:29:49 +0000 (GMT) X-Mailer: emacs 29.0.50 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: linux-mm@kvack.org, akpm@linux-foundation.org Cc: Wei Xu , Huang Ying , Yang Shi , Davidlohr Bueso , Tim C Chen , Michal Hocko , Linux Kernel Mailing List , Hesham Almatary , Dave Hansen , Jonathan Cameron , Alistair Popple , Dan Williams , Johannes Weiner , jvgediya.oss@gmail.com Subject: Re: [PATCH v8 00/12] mm/demotion: Memory tiers and demotion In-Reply-To: <20220704070612.299585-1-aneesh.kumar@linux.ibm.com> References: <20220704070612.299585-1-aneesh.kumar@linux.ibm.com> Date: Mon, 11 Jul 2022 20:59:43 +0530 Message-ID: <87bktvvfa0.fsf@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: _VAiQXu-fU9w_jDvMq5cH9RyID7lC3ch X-Proofpoint-GUID: bG7t0Hnke-2V7rrzR1XmjVeNd1uwmmQm X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.883,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-07-11_19,2022-07-08_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 lowpriorityscore=0 clxscore=1015 mlxscore=0 malwarescore=0 phishscore=0 mlxlogscore=999 impostorscore=0 suspectscore=0 spamscore=0 priorityscore=1501 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2206140000 definitions=main-2207110064 ARC-Authentication-Results: i=1; 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dkim=pass header.d=ibm.com header.s=pp1 header.b=TwSb7TuV; dmarc=pass (policy=none) header.from=ibm.com; spf=pass (imf14.hostedemail.com: domain of aneesh.kumar@linux.ibm.com designates 148.163.156.1 as permitted sender) smtp.mailfrom=aneesh.kumar@linux.ibm.com X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1657553422-162580 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: "Aneesh Kumar K.V" writes: > The current kernel has the basic memory tiering support: Inactive > pages on a higher tier NUMA node can be migrated (demoted) to a lower > tier NUMA node to make room for new allocations on the higher tier > NUMA node. Frequently accessed pages on a lower tier NUMA node can be > migrated (promoted) to a higher tier NUMA node to improve the > performance. > > 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 (e.g. GPU memory) devices, these > memory-only HBM NUMA nodes should be in the top tier, and DRAM nodes > with CPUs are better to be placed into the next lower tier. > > * Also because the current tier hierarchy always puts CPU nodes > into the top tier, when a CPU is hot-added (or hot-removed) and > triggers a memory node from CPU-less into a CPU node (or vice > versa), the memory tier hierarchy gets changed, even though no > memory node is added or removed. This can make the tier > hierarchy unstable and make it difficult to support tier-based > memory accounting. > > * A 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), and has resulted in the feature request for an interface to > override the system-wide, per-node demotion order from the > userspace. 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. > > * There are no interfaces for the userspace to learn about the memory > tier hierarchy in order to optimize its memory allocations. > > This patch series make the creation of memory tiers explicit under > the control of userspace or device driver. > > Memory Tier Initialization > ========================== > > By default, all memory nodes are assigned to the default tier with > tier ID value 200. > > A device driver can move up or down its memory nodes from the default > tier. For example, PMEM can move down its memory nodes below the > default tier, whereas GPU can move up its memory nodes above the > default tier. > > The kernel initialization code makes the decision on which exact tier > a memory node should be assigned to based on the requests from the > device drivers as well as the memory device hardware information > provided by the firmware. > > Hot-adding/removing CPUs doesn't affect memory tier hierarchy. > > Memory Allocation for Demotion > ============================== > This patch series keep the demotion target page allocation logic same. > The demotion page allocation pick the closest NUMA node in the > next lower tier to the current NUMA node allocating pages from. > > This will be later improved to use the same page allocation strategy > using fallback list. > > Sysfs Interface: > ------------- > Listing current list of memory tiers details: > > :/sys/devices/system/memtier$ ls > default_tier max_tier memtier1 power uevent > :/sys/devices/system/memtier$ cat default_tier > memtier200 > :/sys/devices/system/memtier$ cat max_tier > 400 > :/sys/devices/system/memtier$ > > Per node memory tier details: > > For a cpu only NUMA node: > > :/sys/devices/system/node# cat node0/memtier > :/sys/devices/system/node# echo 1 > node0/memtier > :/sys/devices/system/node# cat node0/memtier > :/sys/devices/system/node# > > For a NUMA node with memory: > :/sys/devices/system/node# cat node1/memtier > 1 > :/sys/devices/system/node# ls ../memtier/ > default_tier max_tier memtier1 power uevent > :/sys/devices/system/node# echo 2 > node1/memtier > :/sys/devices/system/node# > :/sys/devices/system/node# ls ../memtier/ > default_tier max_tier memtier1 memtier2 power uevent > :/sys/devices/system/node# cat node1/memtier > 2 > :/sys/devices/system/node# > > Removing a memory tier > :/sys/devices/system/node# cat node1/memtier > 2 > :/sys/devices/system/node# echo 1 > node1/memtier > :/sys/devices/system/node# > :/sys/devices/system/node# cat node1/memtier > 1 > :/sys/devices/system/node# > :/sys/devices/system/node# ls ../memtier/ > default_tier max_tier memtier1 power uevent > :/sys/devices/system/node# > > The above resulted in removal of memtier2 which was created in the earlier step. > > Changes from v7: > * Fix kernel crash with demotion. > * Improve documentation. > > Changes from v6: > * Drop the usage of rank. > * Address other review feedback. > > Changes from v5: > * Remove patch supporting N_MEMORY node removal from memory tiers. memory tiers > are going to be used for features other than demotion. Hence keep all N_MEMORY > nodes in memory tiers irrespective of whether they want to participate in promotion or demotion. > * Add NODE_DATA->memtier > * Rearrage patches to add sysfs files later. > * Add support to create memory tiers from userspace. > * Address other review feedback. > > > Changes from v4: > * Address review feedback. > * Reverse the meaning of "rank": higher rank value means higher tier. > * Add "/sys/devices/system/memtier/default_tier". > * Add node_is_toptier > > v4: > Add support for explicit memory tiers and ranks. > > v3: > - Modify patch 1 subject to make it more specific > - Remove /sys/kernel/mm/numa/demotion_targets interface, use > /sys/devices/system/node/demotion_targets instead and make > it writable to override node_states[N_DEMOTION_TARGETS]. > - Add support to view per node demotion targets via sysfs > > v2: > In v1, only 1st patch of this patch series was sent, which was > implemented to avoid some of the limitations on the demotion > target sharing, however for certain numa topology, the demotion > targets found by that patch was not most optimal, so 1st patch > in this series is modified according to suggestions from Huang > and Baolin. Different examples of demotion list comparasion > between existing implementation and changed implementation can > be found in the commit message of 1st patch. > > > Aneesh Kumar K.V (10): > mm/demotion: Add support for explicit memory tiers > mm/demotion: Move memory demotion related code > mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM > mm/demotion: Add hotplug callbacks to handle new numa node onlined > mm/demotion: Build demotion targets based on explicit memory tiers > mm/demotion: Expose memory tier details via sysfs > mm/demotion: Add per node memory tier attribute to sysfs > mm/demotion: Add pg_data_t member to track node memory tier details > mm/demotion: Update node_is_toptier to work with memory tiers > mm/demotion: Add sysfs ABI documentation > > Jagdish Gediya (2): > mm/demotion: Demote pages according to allocation fallback order > mm/demotion: Add documentation for memory tiering > > .../ABI/testing/sysfs-kernel-mm-memory-tiers | 61 ++ > Documentation/admin-guide/mm/index.rst | 1 + > .../admin-guide/mm/memory-tiering.rst | 192 +++++ > drivers/base/node.c | 42 + > drivers/dax/kmem.c | 6 +- > include/linux/memory-tiers.h | 72 ++ > include/linux/migrate.h | 15 - > include/linux/mmzone.h | 3 + > include/linux/node.h | 5 - > mm/Makefile | 1 + > mm/huge_memory.c | 1 + > mm/memory-tiers.c | 791 ++++++++++++++++++ > mm/migrate.c | 453 +--------- > mm/mprotect.c | 1 + > mm/vmscan.c | 59 +- > mm/vmstat.c | 4 - > 16 files changed, 1215 insertions(+), 492 deletions(-) > create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-memory-tiers > create mode 100644 Documentation/admin-guide/mm/memory-tiering.rst > create mode 100644 include/linux/memory-tiers.h > create mode 100644 mm/memory-tiers.c > Gentle ping. Any objections for this series? -aneesh