memory tier: dax/kmem: introduce an abstract layer for finding, allocating, and putting memory types

Patch series "Improved Memory Tier Creation for CPUless NUMA Nodes", v11.

When a memory device, such as CXL1.1 type3 memory, is emulated as normal
memory (E820_TYPE_RAM), the memory device is indistinguishable from normal
DRAM in terms of memory tiering with the current implementation.  The
current memory tiering assigns all detected normal memory nodes to the
same DRAM tier.  This results in normal memory devices with different
attributions being unable to be assigned to the correct memory tier,
leading to the inability to migrate pages between different types of
memory. 
https://lore.kernel.org/linux-mm/PH0PR08MB7955E9F08CCB64F23963B5C3A860A@PH0PR08MB7955.namprd08.prod.outlook.com/T/

This patchset automatically resolves the issues.  It delays the
initialization of memory tiers for CPUless NUMA nodes until they obtain
HMAT information and after all devices are initialized at boot time,
eliminating the need for user intervention.  If no HMAT is specified, it
falls back to using `default_dram_type`.

Example usecase:
We have CXL memory on the host, and we create VMs with a new system memory
device backed by host CXL memory.  We inject CXL memory performance
attributes through QEMU, and the guest now sees memory nodes with
performance attributes in HMAT.  With this change, we enable the guest
kernel to construct the correct memory tiering for the memory nodes.


This patch (of 2):

Since different memory devices require finding, allocating, and putting
memory types, these common steps are abstracted in this patch, enhancing
the scalability and conciseness of the code.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ho-Ren (Jack) Chuang <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Reviewed-by: Jonathan Cameron <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Aneesh Kumar K.V <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Gregory Price <[email protected]>
Cc: Hao Xiang <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Ravi Jonnalagadda <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vishal Verma <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

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