| Message ID | 20220610135006.182507-1-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm/demotion: Memory tiers and demotion | expand |
On Fri, 10 Jun 2022 19:19:53 +0530 "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> wrote: > 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 (1). > The default tier device has a rank 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 and rank details: > > :/sys/devices/system/memtier$ ls > default_tier max_tier memtier1 power uevent > :/sys/devices/system/memtier$ cat default_tier > memtier1 > :/sys/devices/system/memtier$ cat max_tier > 3 Should this be renamed to max_tiers or tiers_count? Otherwise one might confuse max_tier as the highest allowed tier ID. > :/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# > :/sys/devices/system/node# cat ../memtier/memtier2/rank > 100 > :/sys/devices/system/node# > :/sys/devices/system/node# cat ../memtier/memtier1/rank > 200 > :/sys/devices/system/node# > > Removing a NUMA node from demotion: > :/sys/devices/system/node# cat node1/memtier > 2 > :/sys/devices/system/node# echo none > node1/memtier > :/sys/devices/system/node# > :/sys/devices/system/node# cat node1/memtier > :/sys/devices/system/node# > :/sys/devices/system/node# ls ../memtier/ > default_tier max_tier memtier1 power uevent > :/sys/devices/system/node# > > The above also resulted in removal of memtier2 which was created in > the earlier step. > > > 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 (11): > mm/demotion: Add support for explicit memory tiers > mm/demotion: Move memory demotion related code > mm/demotion: Return error on write to numa_demotion sysfs > mm/demotion/dax/kmem: Set node's memory tier to MEMORY_TIER_PMEM > 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 support for memory tier creation from userspace > 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 | 87 ++ > Documentation/admin-guide/mm/index.rst | 1 + > .../admin-guide/mm/memory-tiering.rst | 181 ++++ > drivers/base/node.c | 39 + > drivers/dax/kmem.c | 4 + > include/linux/memory-tiers.h | 63 ++ > include/linux/migrate.h | 15 - > include/linux/mmzone.h | 3 + > include/linux/node.h | 5 - > mm/Kconfig | 3 + > mm/Makefile | 1 + > mm/huge_memory.c | 1 + > mm/memory-tiers.c | 888 > ++++++++++++++++++ mm/migrate.c | > 453 +-------- mm/mprotect.c | 1 + > mm/vmscan.c | 57 +- > mm/vmstat.c | 4 - > 17 files changed, 1316 insertions(+), 490 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 >