Hi

I also tested the addional cases on arm64

1, 4k page size + devdax + --map=mem

2, 64k page size + devdax + --map=mem

3, 4k page size + devdax + --map=dev

4, 64k page size + devdax + --map=dev

case 4 is important to verify Anshuman's this series.

Host kernel: 5.7-rc3

guest kernel: 5.7-rc5 with this series

ndctl: https://github.com/pmem/ndctl/tree/c7767834871

On the guest:

1. ./ndctl/.libs/ndctl create-namespace -e namespace0.0 --mode=devdax --map=dev -s 1g -f -v -a 64K

 echo dax0.0 > /sys/bus/dax/drivers/device_dax/unbind
 echo dax0.0 > /sys/bus/dax/drivers/kmem/new_id

The 1g block was added

2. echo 0 > /sys/devices/system/memory/memory10/online

modprobe -r dax_pmem

The 1g block was removed

Some minor fix should be applied which is not relevant to this series itself. e.g numa id

---
Cheers,
Justin (Jia He)

This series enables vmemmap backing memory allocation from device memory
ranges on arm64. But before that, it enables vmemmap_populate_basepages()
and vmemmap_alloc_block_buf() to accommodate struct vmem_altmap based
alocation requests.

This series applies on 5.8-rc1.

Pending Question:

altmap_alloc_block_buf() does not have any other remaining users in the
tree after this change. Should it be converted into a static function and
it's declaration be dropped from the header (include/linux/mm.h). Avoided
doing so because I was not sure if there are any off-tree users or not.

Changes in V3:

- Dropped comment from free_hotplug_page_range() per Robin
- Modified comment in unmap_hotplug_range() per Robin
- Enabled altmap support in vmemmap_alloc_block_buf() per Robin

Changes in V2: (https://lkml.org/lkml/2020/3/4/475)

- Rebased on latest hot-remove series (v14) adding P4D page table support

Changes in V1: (https://lkml.org/lkml/2020/1/23/12)

- Added an WARN_ON() in unmap_hotplug_range() when altmap is
  provided without the page table backing memory being freed

Changes in RFC V2: (https://lkml.org/lkml/2019/10/21/11)

- Changed the commit message on 1/2 patch per Will
- Changed the commit message on 2/2 patch as well
- Rebased on arm64 memory hot remove series (v10)

RFC V1: (https://lkml.org/lkml/2019/6/28/32)

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-ia64@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: x86@kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org

Anshuman Khandual (3):
  mm/sparsemem: Enable vmem_altmap support in vmemmap_populate_basepages()
  mm/sparsemem: Enable vmem_altmap support in vmemmap_alloc_block_buf()
  arm64/mm: Enable vmem_altmap support for vmemmap mappings

 arch/arm64/mm/mmu.c       | 59 ++++++++++++++++++++++++++-------------
 arch/ia64/mm/discontig.c  |  2 +-
 arch/powerpc/mm/init_64.c | 10 +++----
 arch/riscv/mm/init.c      |  2 +-
 arch/x86/mm/init_64.c     | 12 ++++----
 include/linux/mm.h        |  8 ++++--
 mm/sparse-vmemmap.c       | 38 ++++++++++++++++++++-----
 7 files changed, 87 insertions(+), 44 deletions(-)

--