On Wed, 2022-06-08 at 10:28 +0530, Aneesh Kumar K V wrote: > On 6/8/22 3:02 AM, Yang Shi wrote: > > 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. > > > > This was added so that we could avoid doing multiple > > #if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA) > > Initially I had that as def_bool y and depends on MIGRATION && NUMA. But > it was later suggested that def_bool is not recommended for newer config. > > How about > > config TIERED_MEMORY > bool "Support for explicit memory tiers" Need to remove this line too to make it invisible for users? Best Regards, HUang, Ying > - 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. > + def_bool MIGRATION && NUMA > > config HUGETLB_PAGE_SIZE_VARIABLE > def_bool n > > ie, we just make it a Kconfig variable without exposing it to the user? > > -aneesh
