[v4 0/4] mm: hugetlb: Skip initialization of gigantic tail struct pages if freed by HVO

[Usama Arif <usama.arif@bytedance.com>]

This series moves the boot time initialization of tail struct pages of a
gigantic page to later on in the boot. Only the
HUGETLB_VMEMMAP_RESERVE_SIZE / sizeof(struct page) - 1 tail struct pages
are initialized at the start. If HVO is successful, then no more tail struct
pages need to be initialized. For a 1G hugepage, this series avoid
initialization of 262144 - 63 = 262081 struct pages per hugepage.

When tested on a 512G system (which can allocate max 500 1G hugepages), the
kexec-boot time with HVO and DEFERRED_STRUCT_PAGE_INIT enabled without this
patchseries to running init is 3.9 seconds. With this patch it is 1.2 seconds.
This represents an approximately 70% reduction in boot time and will
significantly reduce server downtime when using a large number of
gigantic pages.

Thanks,
Usama

[v3->v4]:
- rebase ontop of patch "hugetlb: set hugetlb page flag before optimizing vmemmap".
- freeze head struct page ref count.
- Change order of operations to initialize head struct page -> initialize
the necessary tail struct pages -> attempt HVO -> initialize the rest of the
tail struct pages if HVO fails.
- (Mike Rapoport and Muchun Song) remove "_vmemmap" suffix from memblock reserve
noinit flags anf functions.

[v2->v3]:
- (Muchun Song) skip prep of struct pages backing gigantic hugepages
at boot time only.
- (Muchun Song) move initialization of tail struct pages to after
HVO is attempted.

[v1->v2]:
- (Mike Rapoport) Code quality improvements (function names, arguments,
comments).

[RFC->v1]:
- (Mike Rapoport) Change from passing hugepage_size in
memblock_alloc_try_nid_raw for skipping struct page initialization to
using MEMBLOCK_RSRV_NOINIT flag

Usama Arif (4):
  mm: hugetlb_vmemmap: Use nid of the head page to reallocate it
  memblock: pass memblock_type to memblock_setclr_flag
  memblock: introduce MEMBLOCK_RSRV_NOINIT flag
  mm: hugetlb: Skip initialization of gigantic tail struct pages if
    freed by HVO

 include/linux/memblock.h |  9 ++++++
 mm/hugetlb.c             | 61 ++++++++++++++++++++++++++++++++++------
 mm/hugetlb_vmemmap.c     |  4 +--
 mm/hugetlb_vmemmap.h     |  9 +++---
 mm/internal.h            |  3 ++
 mm/memblock.c            | 48 ++++++++++++++++++++++---------
 mm/mm_init.c             |  2 +-
 7 files changed, 107 insertions(+), 29 deletions(-)

-- 
2.25.1