LKML: Barry Song: Re: [RFC PATCH 0/8] mm/vmalloc: Speed up ioremap, vmalloc and vmap with contiguous memory

On Wed, Apr 8, 2026 at 5:14 PM Dev Jain <dev.jain@arm.com> wrote:
>
>
>
> On 08/04/26 8:21 am, Barry Song (Xiaomi) wrote:
> > This patchset accelerates ioremap, vmalloc, and vmap when the memory
> > is physically fully or partially contiguous. Two techniques are used:
> >
> > 1. Avoid page table zigzag when setting PTEs/PMDs for multiple memory
> > segments
> > 2. Use batched mappings wherever possible in both vmalloc and ARM64
> > layers
> >
> > Patches 1–2 extend ARM64 vmalloc CONT-PTE mapping to support multiple
> > CONT-PTE regions instead of just one.
> >
> > Patches 3–4 extend vmap_small_pages_range_noflush() to support page
> > shifts other than PAGE_SHIFT. This allows mapping multiple memory
> > segments for vmalloc() without zigzagging page tables.
> >
> > Patches 5–8 add huge vmap support for contiguous pages. This not only
> > improves performance but also enables PMD or CONT-PTE mapping for the
> > vmapped area, reducing TLB pressure.
> >
> > Many thanks to Xueyuan Chen for his substantial testing efforts
> > on RK3588 boards.
> >
> > On the RK3588 8-core ARM64 SoC, with tasks pinned to CPU2 and
> > the performance CPUfreq policy enabled, Xueyuan’s tests report:
> >
> > * ioremap(1 MB): 1.2× faster
> > * vmalloc(1 MB) mapping time (excluding allocation) with
> > VM_ALLOW_HUGE_VMAP: 1.5× faster
> > * vmap(): 5.6× faster when memory includes some order-8 pages,
> > with no regression observed for order-0 pages
> >
> > Barry Song (Xiaomi) (8):
> > 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 vmap_small_pages_range_noflush() to support larger
> > page_shift sizes
> > mm/vmalloc: Eliminate page table zigzag for huge vmalloc mappings
> > mm/vmalloc: map contiguous pages in batches for vmap() if possible
> > mm/vmalloc: align vm_area so vmap() can batch mappings
> > mm/vmalloc: Coalesce same page_shift mappings in vmap to avoid pgtable
> > zigzag
> > mm/vmalloc: Stop scanning for compound pages after encountering small
> > pages in vmap
> >
> > arch/arm64/include/asm/vmalloc.h | 6 +-
> > arch/arm64/mm/hugetlbpage.c | 10 ++
> > mm/vmalloc.c | 178 +++++++++++++++++++++++++------
> > 3 files changed, 161 insertions(+), 33 deletions(-)
> >
>
> On Linux VM on Apple M3, running mm-selftests:

Dev, thanks for your report. Sorry for the silly typo—
Xueyuan’s vmalloc/vmap tests don’t trigger that case yet.

it should be fixed by:

diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
index bf31c11ebd3b..25b9fce1ec6a 100644
--- a/arch/arm64/mm/hugetlbpage.c
+++ b/arch/arm64/mm/hugetlbpage.c
@@ -110,7 +110,7 @@ static inline int num_contig_ptes(unsigned long
size, size_t *pgsize)
contig_ptes = CONT_PTES;
break;
default:
- if (size < CONT_PMD_SIZE && size > 0 &&
+ if (size < PMD_SIZE && size > 0 &&
IS_ALIGNED(size, CONT_PTE_SIZE)) {
contig_ptes = size >> PAGE_SHIFT;
*pgsize = PAGE_SIZE;
@@ -365,7 +365,7 @@ pte_t arch_make_huge_pte(pte_t entry, unsigned int
shift, vm_flags_t flags)
case CONT_PTE_SIZE:
return pte_mkcont(entry);
default:
- if (pagesize < CONT_PMD_SIZE && pagesize > 0 &&
+ if (pagesize < PMD_SIZE && pagesize > 0 &&
IS_ALIGNED(pagesize, CONT_PTE_SIZE))
return pte_mkcont(entry);

> ./run_vmtests.sh -t "hugetlb"
>
> TAP version 13
> # -----------------------
> # running ./hugepage-mmap
> # -----------------------
> # TAP version 13
> # 1..1
> # # Returned address is 0xffffe7c00000
>
>
>
> [ 30.884630] kernel BUG at mm/page_table_check.c:86!
> [ 30.884701] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
> [ 30.886803] Modules linked in:
> [ 30.887217] CPU: 3 UID: 0 PID: 1869 Comm: hugepage-mmap Not tainted 7.0.0-rc5+ #86 PREEMPT
> [ 30.888218] Hardware name: linux,dummy-virt (DT)
> [ 30.889413] pstate: a1400005 (NzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> [ 30.889901] pc : page_table_check_clear.part.0+0x128/0x1a0
> [ 30.890337] lr : page_table_check_clear.part.0+0x7c/0x1a0
> [ 30.890714] sp : ffff800084da3ad0
> [ 30.890946] x29: ffff800084da3ad0 x28: 0000000000000001 x27: 0010000000000001
> [ 30.891434] x26: 0040000000000040 x25: ffffa06bb8fb9000 x24: 00000000ffffffff
> [ 30.891932] x23: 0000000000000001 x22: 0000000000000000 x21: ffffa06bb8997810
> [ 30.892514] x20: 0000000000113e39 x19: 0000000000113e38 x18: 0000000000000000
> [ 30.893007] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
> [ 30.893500] x14: ffffa06bb7013780 x13: 0000fffff7f90fff x12: 0000000000000000
> [ 30.893990] x11: 1fffe0001a1282c1 x10: ffff0000d094160c x9 : ffffa06bb568a858
> [ 30.894479] x8 : ffff5f95c8474000 x7 : 0000000000000000 x6 : ffff00017fffc500
> [ 30.894973] x5 : ffff000191208fc0 x4 : 0000000000000000 x3 : 0000000000004000
> [ 30.895449] x2 : 0000000000000000 x1 : 00000000ffffffff x0 : ffff0000c071f1b8
> [ 30.895875] Call trace:
> [ 30.896027] page_table_check_clear.part.0+0x128/0x1a0 (P)
> [ 30.896369] page_table_check_clear+0xc8/0x138
> [ 30.896776] __page_table_check_ptes_set+0xe4/0x1e8
> [ 30.897073] __set_ptes_anysz+0x2e4/0x308
> [ 30.897327] set_huge_pte_at+0xec/0x210
> [ 30.897561] hugetlb_no_page+0x1ec/0x8e0
> [ 30.897807] hugetlb_fault+0x188/0x740
> [ 30.898036] handle_mm_fault+0x294/0x2c0
> [ 30.898283] do_page_fault+0x120/0x748
> [ 30.898539] do_translation_fault+0x68/0x90
> [ 30.898796] do_mem_abort+0x4c/0xa8
> [ 30.899011] el0_da+0x2c/0x90
> [ 30.899205] el0t_64_sync_handler+0xd0/0xe8
> [ 30.899461] el0t_64_sync+0x198/0x1a0
> [ 30.899688] Code: 91001021 b8f80022 51000441 36fffd41 (d4210000)
> [ 30.900053] ---[ end trace 0000000000000000 ]---
>
>
>
> The bug is at
>
> BUG_ON(atomic_dec_return(&ptc->file_map_count) < 0);
>
> My tree is mm-unstable, commit 3fa44141e0bb.
>

Thanks
Barry