[PATCH v3 0/6] mm/vmalloc: Speed up ioremap, vmalloc and vmap with contiguous memory

[Wen Jiang]

From: jiangwen6 <jiangwen6 at xiaomi.com>

This patchset accelerates ioremap, vmalloc, and vmap when the memory
is physically fully or partially contiguous. Two techniques are used:

1. Avoid page table rewalk when setting PTEs/PMDs for multiple memory
   segments
2. Use batched mappings wherever possible in both vmalloc and ARM64
   layers

Besides accelerating the mapping path, this also enables large
mappings (PMD and cont-PTE) for vmap, which are currently not
supported.

Patches 1-2 extend ARM64 vmalloc CONT-PTE mapping to support multiple
CONT-PTE regions instead of just one.

Patch 3 extracts a common helper vmap_set_ptes() that consolidates PTE
mapping logic between the ioremap and vmalloc/vmap paths, handling both
CONT_PTE and regular PTE mappings. This prepares for the next patch.

Patch 4 extends the page table walk path to support page shifts other
than PAGE_SHIFT and eliminates the page table rewalk for huge vmalloc
mappings. The function is renamed from vmap_small_pages_range_noflush()
to vmap_pages_range_noflush_walk().

Patches 5-6 add huge vmap support for contiguous pages, including
support for non-compound pages with pfn alignment verification.

On the RK3588 8-core ARM64 SoC, with tasks pinned to a little core and
the performance CPUfreq policy enabled, benchmark results:

* ioremap(1 MB): 1.35x faster (3407 ns -> 2526 ns)
* vmalloc(1 MB) mapping time (excluding allocation) with
  VM_ALLOW_HUGE_VMAP: 1.42x faster (5.00 us -> 3.53us)
* vmap(100MB) with order-8 pages: 8.3x faster (1235 us -> 149 us)

Many thanks to Xueyuan Chen for his testing efforts on RK3588 boards.

Changes since v2:
- Use __fls instead of fls in arch_vmap_pte_range_map_size (patch 2)
- Add WARN_ON checks in vmap_pages_pmd_range (patch 4)
- Fix flush_cache_vmap to use saved start address instead of the
  already-advanced addr (patch 5)
- Rename __vmap_huge() to vmap_batched() (patch 5)
- Add caller parameter and unroll while(1) loop (patch 5)
- Squash patch 7 into patch 5 (stop scanning for compound pages after
  encountering small pages)

Changes since v1:
- Fix condition order and use PMD_SIZE instead of CONT_PMD_SIZE in
  patch 1 (Dev Jain)
- Squash patch 3+4 and patch 5+7 (Dev Jain)
- Replace "zigzag" with "page table rewalk" in commit messages
  (Dev Jain)
- Rename vmap_small_pages_range_noflush() to
  vmap_pages_range_noflush_walk() (Dev Jain)
- Extract vmap_set_ptes() as a new patch to consolidate PTE mapping
  logic between vmap_pte_range() and vmap_pages_pte_range(), handling
  both CONT_PTE and regular mappings (Mike Rapoport)
- Support non-compound pages in get_vmap_batch_order() by falling
  back to physical contiguity scanning with pfn alignment check
  (Dev Jain, Uladzislau Rezki)
- In get_vmap_batch_order(), filter out orders that the architecture
  cannot batch by checking arch_vmap_pte_supported_shift() directly.
  This avoids overhead for orders 1-3 on ARM64 CONT_PTE with 4K
  pages. (patch 5)

Barry Song (Xiaomi) (5):
  arm64/hugetlb: Extend batching of multiple CONT_PTE in a single PTE
    setup
  arm64/vmalloc: Allow arch_vmap_pte_range_map_size to batch multiple
    CONT_PTE
  mm/vmalloc: Extend page table walk to support larger page_shift sizes
    and eliminate page table rewalk
  mm/vmalloc: map contiguous pages in batches for vmap() if possible
  mm/vmalloc: align vm_area so vmap() can batch mappings

Wen Jiang (1):
  mm/vmalloc: Extract vmap_set_ptes() to consolidate PTE mapping logic

 arch/arm64/include/asm/vmalloc.h |   6 +-
 arch/arm64/mm/hugetlbpage.c      |  10 ++
 mm/vmalloc.c                     | 235 ++++++++++++++++++++++++-------
 3 files changed, 201 insertions(+), 50 deletions(-)

-- 
2.34.1