[PATCH 00/12] kho: make boot time huge page allocation work nicely with KHO

[Pratyush Yadav]

From: "Pratyush Yadav (Google)" <pratyush at kernel.org>

Hi,

Gigantic huge page allocation is somewhat broken currently with KHO.

First, they break scratch size accounting. Since they are allocated
using the memblock alloc APIs, they count towards RSRV_KERN, and this
scratch size when using scratch_scale. This means if huge pages take a
large enough chunk of system memory scratch size will blow up and fail
to allocate.

Second, scratch can not contain preserved memory, and if hugepages are
allocated from scratch, they will fail to be preserved with the upcoming
hugetlb preservation series [0].

Fix this by introducing the concept of extended scratch areas. They are
areas that the kernel discovers on boot by walking the radix tree and
finding free memory ranges. See patch 10 for more details.

Discovering the scratch areas needs some changes to the radix tree APIs
and to memblock. Patches 1-8 do that.

Patch 9 introduces extended scratch to memblock.

Patch 10 adds the extended scratch discovery logic.

Patch 11 cleans up the preserved memory map API.

Finally, patch 12 puts all the pieces together and uses only extended
scratch for hugepage allocation and does not count then towards
RSRV_KERN.

[0] https://lore.kernel.org/linux-mm/20251206230222.853493-1-pratyush@kernel.org/T/#u

Regards,
Pratyush Yadav

Pratyush Yadav (Google) (12):
  kho: generalize radix tree APIs
  kho: store incoming radix tree in kho_in
  kho: add a struct for radix callbacks
  kho: add callback for table pages
  kho: add data argument to radix walk callback
  kho: allow early-boot usage of the KHO radix tree
  kho: allow destroying KHO radix tree
  kho: add kho_radix_init_tree()
  memblock: introduce MEMBLOCK_KHO_SCRATCH_EXT
  kho: extended scratch
  kho: return virtual address of mem_map
  mm/hugetlb: make bootmem allocation work with KHO

 include/linux/kexec_handover.h     |   1 +
 include/linux/kho_radix_tree.h     |  44 ++--
 include/linux/memblock.h           |  14 ++
 kernel/liveupdate/kexec_handover.c | 389 ++++++++++++++++++++++-------
 mm/hugetlb.c                       |  19 +-
 mm/memblock.c                      | 177 ++++++++++---
 mm/mm_init.c                       |   1 +
 7 files changed, 489 insertions(+), 156 deletions(-)


base-commit: eee13213401bafb7ffe3b447adffb1f570b9d813
-- 
2.54.0.545.g6539524ca2-goog