On Fri, Jun 3, 2022 at 6:43 AM Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> 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 <weixugc@xxxxxxxxxx> at [1]. > > [1] https://lore.kernel.org/linux-mm/CAAPL-u9Wv+nH1VOZTj=9p9S70Y3Qz3+63EkqncRDdHfubsrjfw@xxxxxxxxxxxxxx > > Suggested-by: Wei Xu <weixugc@xxxxxxxxxx> > Signed-off-by: Jagdish Gediya <jvgediya@xxxxxxxxxxxxx> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> > --- > 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. > + > config HUGETLB_PAGE_SIZE_VARIABLE > def_bool n > help > diff --git a/mm/Makefile b/mm/Makefile > index 6f9ffa968a1a..482557fbc9d1 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -92,6 +92,7 @@ obj-$(CONFIG_KFENCE) += kfence/ > obj-$(CONFIG_FAILSLAB) += failslab.o > obj-$(CONFIG_MEMTEST) += memtest.o > obj-$(CONFIG_MIGRATION) += migrate.o > +obj-$(CONFIG_TIERED_MEMORY) += memory-tiers.o > obj-$(CONFIG_DEVICE_MIGRATION) += migrate_device.o > obj-$(CONFIG_TRANSPARENT_HUGEPAGE) += huge_memory.o khugepaged.o > obj-$(CONFIG_PAGE_COUNTER) += page_counter.o > diff --git a/mm/memory-tiers.c b/mm/memory-tiers.c > new file mode 100644 > index 000000000000..7de18d94a08d > --- /dev/null > +++ b/mm/memory-tiers.c > @@ -0,0 +1,188 @@ > +// SPDX-License-Identifier: GPL-2.0 > +#include <linux/types.h> > +#include <linux/device.h> > +#include <linux/nodemask.h> > +#include <linux/slab.h> > +#include <linux/memory-tiers.h> > + > +struct memory_tier { > + struct list_head list; > + struct device dev; > + nodemask_t nodelist; > + int rank; > +}; > + > +#define to_memory_tier(device) container_of(device, struct memory_tier, dev) > + > +static struct bus_type memory_tier_subsys = { > + .name = "memtier", > + .dev_name = "memtier", > +}; > + > +static DEFINE_MUTEX(memory_tier_lock); > +static LIST_HEAD(memory_tiers); > + > + > +static ssize_t nodelist_show(struct device *dev, > + struct device_attribute *attr, char *buf) > +{ > + struct memory_tier *memtier = to_memory_tier(dev); > + > + return sysfs_emit(buf, "%*pbl\n", > + nodemask_pr_args(&memtier->nodelist)); > +} > +static DEVICE_ATTR_RO(nodelist); > + > +static ssize_t rank_show(struct device *dev, > + struct device_attribute *attr, char *buf) > +{ > + struct memory_tier *memtier = to_memory_tier(dev); > + > + return sysfs_emit(buf, "%d\n", memtier->rank); > +} > +static DEVICE_ATTR_RO(rank); > + > +static struct attribute *memory_tier_dev_attrs[] = { > + &dev_attr_nodelist.attr, > + &dev_attr_rank.attr, > + NULL > +}; > + > +static const struct attribute_group memory_tier_dev_group = { > + .attrs = memory_tier_dev_attrs, > +}; > + > +static const struct attribute_group *memory_tier_dev_groups[] = { > + &memory_tier_dev_group, > + NULL > +}; > + > +static void memory_tier_device_release(struct device *dev) > +{ > + struct memory_tier *tier = to_memory_tier(dev); > + > + kfree(tier); > +} > + > +/* > + * Keep it simple by having direct mapping between > + * tier index and rank value. > + */ > +static inline int get_rank_from_tier(unsigned int tier) > +{ > + switch (tier) { > + case MEMORY_TIER_HBM_GPU: > + return MEMORY_RANK_HBM_GPU; > + case MEMORY_TIER_DRAM: > + return MEMORY_RANK_DRAM; > + case MEMORY_TIER_PMEM: > + return MEMORY_RANK_PMEM; > + } > + > + return 0; > +} > + > +static void insert_memory_tier(struct memory_tier *memtier) > +{ > + struct list_head *ent; > + struct memory_tier *tmp_memtier; > + > + list_for_each(ent, &memory_tiers) { > + tmp_memtier = list_entry(ent, struct memory_tier, list); > + if (tmp_memtier->rank < memtier->rank) { > + list_add_tail(&memtier->list, ent); > + return; > + } > + } > + list_add_tail(&memtier->list, &memory_tiers); > +} > + > +static struct memory_tier *register_memory_tier(unsigned int tier) > +{ > + int error; > + struct memory_tier *memtier; > + > + if (tier >= MAX_MEMORY_TIERS) > + return NULL; > + > + memtier = kzalloc(sizeof(struct memory_tier), GFP_KERNEL); > + if (!memtier) > + return NULL; > + > + memtier->dev.id = tier; > + memtier->rank = get_rank_from_tier(tier); > + memtier->dev.bus = &memory_tier_subsys; > + memtier->dev.release = memory_tier_device_release; > + memtier->dev.groups = memory_tier_dev_groups; > + > + insert_memory_tier(memtier); > + > + error = device_register(&memtier->dev); > + if (error) { > + list_del(&memtier->list); > + put_device(&memtier->dev); > + return NULL; > + } > + return memtier; > +} > + > +__maybe_unused // temporay to prevent warnings during bisects > +static void unregister_memory_tier(struct memory_tier *memtier) > +{ > + list_del(&memtier->list); > + device_unregister(&memtier->dev); > +} > + > +static ssize_t > +max_tier_show(struct device *dev, struct device_attribute *attr, char *buf) > +{ > + return sysfs_emit(buf, "%d\n", MAX_MEMORY_TIERS); > +} > +static DEVICE_ATTR_RO(max_tier); > + > +static ssize_t > +default_tier_show(struct device *dev, struct device_attribute *attr, char *buf) > +{ > + return sysfs_emit(buf, "memtier%d\n", DEFAULT_MEMORY_TIER); > +} > +static DEVICE_ATTR_RO(default_tier); > + > +static struct attribute *memory_tier_attrs[] = { > + &dev_attr_max_tier.attr, > + &dev_attr_default_tier.attr, > + NULL > +}; > + > +static const struct attribute_group memory_tier_attr_group = { > + .attrs = memory_tier_attrs, > +}; > + > +static const struct attribute_group *memory_tier_attr_groups[] = { > + &memory_tier_attr_group, > + NULL, > +}; > + > +static int __init memory_tier_init(void) > +{ > + int ret; > + struct memory_tier *memtier; > + > + ret = subsys_system_register(&memory_tier_subsys, memory_tier_attr_groups); > + if (ret) > + panic("%s() failed to register subsystem: %d\n", __func__, ret); > + > + /* > + * Register only default memory tier to hide all empty > + * memory tier from sysfs. > + */ > + memtier = register_memory_tier(DEFAULT_MEMORY_TIER); > + if (!memtier) > + panic("%s() failed to register memory tier: %d\n", __func__, ret); > + > + /* CPU only nodes are not part of memory tiers. */ > + memtier->nodelist = node_states[N_MEMORY]; > + > + return 0; > +} > +subsys_initcall(memory_tier_init); > + > -- > 2.36.1 >
