| Message ID | 20220812055710.357820-1-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | mm/demotion: Memory tiers and demotion | expand |
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> 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 highest 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 implementation 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-backed memory-only node on a virtual > machine) and that 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 nodes with shortest distance on the > next lower tier as defined by the demotion path, not any other node from any > lower tier. This strict, 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. > > This patch series make the creation of memory tiers explicit under > the control of device driver. > > Memory Tier Initialization > ========================== > > Linux kernel presents memory devices as NUMA nodes and each memory device is of > a specific type. The memory type of a device is represented by its abstract > distance. A memory tier corresponds to a range of abstract distance. This allows > for classifying memory devices with a specific performance range into a memory > tier. > > By default, all memory nodes are assigned to the default tier with > abstract distance 512. > > A device driver can move its memory nodes from the default tier. For example, > PMEM can move its memory nodes below the default tier, whereas GPU can move 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. > > Changes from v13 > * Address review feedback. > * Add path dropping memtier from struct memory_dev_type > > Changes from v12 > * Fix kernel crash on module unload > * Address review feedback. > * Add node_random patch to this series based on review feedback > > Changes from v11: > * smaller abstract distance imply faster(higher) memory tier. > > Changes from v10: > * rename performance level to abstract distance > * Thanks to all the good feedback from Huang, Ying <ying.huang@intel.com>. > Updated the patchset to cover most of the review feedback. > > Changes from v9: > * Use performance level for initializing memory tiers. > > Changes from v8: > * Drop the sysfs interface patches and related documentation changes. > > 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 (9): > mm/demotion: Add support for explicit memory tiers > mm/demotion: Move memory demotion related code > mm/demotion: Add hotplug callbacks to handle new numa node onlined > mm/demotion/dax/kmem: Set node's abstract distance to > MEMTIER_DEFAULT_DAX_ADISTANCE > mm/demotion: Build demotion targets based on explicit memory tiers > mm/demotion: Add pg_data_t member to track node memory tier details > mm/demotion: Drop memtier from memtype > mm/demotion: Update node_is_toptier to work with memory tiers > lib/nodemask: Optimize node_random for nodemask with single NUMA node > > Jagdish Gediya (1): > mm/demotion: Demote pages according to allocation fallback order > > drivers/dax/kmem.c | 42 ++- > include/linux/memory-tiers.h | 99 ++++++ > include/linux/migrate.h | 15 - > include/linux/mmzone.h | 3 + > include/linux/node.h | 5 - > include/linux/nodemask.h | 15 +- > mm/Makefile | 1 + > mm/huge_memory.c | 1 + > mm/memory-tiers.c | 645 +++++++++++++++++++++++++++++++++++ > mm/migrate.c | 453 +----------------------- > mm/mprotect.c | 1 + > mm/vmscan.c | 59 +++- > mm/vmstat.c | 4 - > 13 files changed, 846 insertions(+), 497 deletions(-) > create mode 100644 include/linux/memory-tiers.h > create mode 100644 mm/memory-tiers.c Except some minor comments, the series looks good to me. Thanks! Feel free to add Reviewed-by: "Huang, Ying" <ying.huang@intel.com> for the whole series. Best Regards, Huang, Ying
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 highest 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 implementation 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-backed memory-only node on a virtual machine) and that 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 nodes with shortest distance on the next lower tier as defined by the demotion path, not any other node from any lower tier. This strict, 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. This patch series make the creation of memory tiers explicit under the control of device driver. Memory Tier Initialization ========================== Linux kernel presents memory devices as NUMA nodes and each memory device is of a specific type. The memory type of a device is represented by its abstract distance. A memory tier corresponds to a range of abstract distance. This allows for classifying memory devices with a specific performance range into a memory tier. By default, all memory nodes are assigned to the default tier with abstract distance 512. A device driver can move its memory nodes from the default tier. For example, PMEM can move its memory nodes below the default tier, whereas GPU can move 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. Changes from v13 * Address review feedback. * Add path dropping memtier from struct memory_dev_type Changes from v12 * Fix kernel crash on module unload * Address review feedback. * Add node_random patch to this series based on review feedback Changes from v11: * smaller abstract distance imply faster(higher) memory tier. Changes from v10: * rename performance level to abstract distance * Thanks to all the good feedback from Huang, Ying <ying.huang@intel.com>. Updated the patchset to cover most of the review feedback. Changes from v9: * Use performance level for initializing memory tiers. Changes from v8: * Drop the sysfs interface patches and related documentation changes. 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 (9): mm/demotion: Add support for explicit memory tiers mm/demotion: Move memory demotion related code mm/demotion: Add hotplug callbacks to handle new numa node onlined mm/demotion/dax/kmem: Set node's abstract distance to MEMTIER_DEFAULT_DAX_ADISTANCE mm/demotion: Build demotion targets based on explicit memory tiers mm/demotion: Add pg_data_t member to track node memory tier details mm/demotion: Drop memtier from memtype mm/demotion: Update node_is_toptier to work with memory tiers lib/nodemask: Optimize node_random for nodemask with single NUMA node Jagdish Gediya (1): mm/demotion: Demote pages according to allocation fallback order drivers/dax/kmem.c | 42 ++- include/linux/memory-tiers.h | 99 ++++++ include/linux/migrate.h | 15 - include/linux/mmzone.h | 3 + include/linux/node.h | 5 - include/linux/nodemask.h | 15 +- mm/Makefile | 1 + mm/huge_memory.c | 1 + mm/memory-tiers.c | 645 +++++++++++++++++++++++++++++++++++ mm/migrate.c | 453 +----------------------- mm/mprotect.c | 1 + mm/vmscan.c | 59 +++- mm/vmstat.c | 4 - 13 files changed, 846 insertions(+), 497 deletions(-) create mode 100644 include/linux/memory-tiers.h create mode 100644 mm/memory-tiers.c