On Fri, 2022-05-27 at 17:55 +0530, Aneesh Kumar K.V wrote: > From: Jagdish Gediya <jvgediya@xxxxxxxxxxxxx> > > 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 adds below sysfs interface which is read-only and > can be used to read nodes available in specific tier. > > /sys/devices/system/memtier/memtierN/nodelist > > Tier 0 is the highest tier, while tier MAX_MEMORY_TIERS - 1 is the > lowest tier. The absolute value of a tier id number has no specific > meaning. what matters is the relative order of the tier id numbers. > > All the tiered memory code is guarded by CONFIG_TIERED_MEMORY. > Default number of memory tiers are MAX_MEMORY_TIERS(3). All the > nodes are by default assigned to DEFAULT_MEMORY_TIER(1). > > Default memory tier can be read from, > /sys/devices/system/memtier/default_tier > > Max memory tier can be read from, > /sys/devices/system/memtier/max_tiers > > This patch implements the RFC spec sent by Wei Xu <weixugc@xxxxxxxxxx> at [1]. > > [1] https://lore.kernel.org/linux-mm/CAAPL-u-DGLcKRVDnChN9ZhxPkfxQvz9Sb93kVoX_4J2oiJSkUw@xxxxxxxxxxxxxx/ > > Signed-off-by: Jagdish Gediya <jvgediya@xxxxxxxxxxxxx> > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> IMHO, we should change the kernel internal implementation firstly, then implement the kerne/user space interface. That is, make memory tier explicit inside kernel, then expose it to user space. Best Regards, Huang, Ying [snip]
