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    SubjectRe: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers
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    On Tue, 2022-06-07 at 14:32 -0700, Yang Shi wrote:
    > On Fri, Jun 3, 2022 at 6:43 AM Aneesh Kumar K.V
    > <aneesh.kumar@linux.ibm.com> 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@google.com> at [1].
    > >
    > > [1] https://lore.kernel.org/linux-mm/CAAPL-u9Wv+nH1VOZTj=9p9S70Y3Qz3+63EkqncRDdHfubsrjfw@mail.gmail.com
    > >
    > > Suggested-by: Wei Xu <weixugc@google.com>
    > > Signed-off-by: Jagdish Gediya <jvgediya@linux.ibm.com>
    > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
    > > ---
    > >  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.

    I think so too. At least it appears unnecessary to let the user turn
    on/off it at configuration time.

    All the code should be enclosed by #if defined(CONFIG_NUMA) &&
    defined(CONIFIG_MIGRATION). So we will not waste memory in small
    systems.

    Best Regards,
    Huang, Ying

    > > +
    > >  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
    > >


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