Module vmalloc 

VM-backed allocator for large heap objects.

Provides virtually contiguous allocations backed by individually allocated physical pages. Unlike the buddy allocator, vmalloc does not require physically contiguous memory : it maps each page individually into a dedicated kernel virtual memory arena.

Arena layout

VMALLOC_VIRT_START = 0xffffc000_0000_0000  (256 GiB boundary)
VMALLOC_SIZE       = 1 GiB
VMALLOC_VIRT_END   = 0xffffc040_0000_0000

This region sits well above the HHDM direct map (starting at 0xffff8000_0000_0000) and kernel code/data.

Allocation strategy

1. Allocate backing physical pages individually from the frame allocator.
2. Reserve a virtually contiguous range from the vmalloc extent allocator.
3. Map each page into the kernel page tables at the virtual address.

Deallocation

1. Unmap each page from the kernel page tables.
2. Flush stale TLB entries across CPUs for the unmapped range.
3. Return the virtual range to the extent allocator.
4. Free each physical page back to the frame allocator.

Metadata model

The allocator no longer uses a fixed allocation-record table or a bitmap. It maintains:

• a sorted free-extent list;
• a sorted active-allocation list;
• a metadata node pool carved from raw buddy pages, independent from the general kernel heap.

This removes the old fixed-slot ceiling and keeps vmalloc bookkeeping from recursing back into heap allocation.

Thread safety

Protected by a single SpinLock<Vmalloc>. IRQs are disabled during allocation to prevent deadlock with the buddy allocator.

Structs

VmallocAttr

Attribution snapshot captured at vmalloc time.

VmallocDiagSnapshot

VmallocFailureSnapshot

VmallocLiveAllocationSnapshot

Enums

VmallocAllocBackend

VmallocError

Constants

VMALLOC_SIZE

Total size of the vmalloc arena: 1 GiB.

VMALLOC_VIRT_END

End virtual address of the vmalloc arena.

VMALLOC_VIRT_START

Base virtual address of the vmalloc arena. Placed at 0xffffc000_0000_0000 : well above the HHDM direct map.

Statics

VMALLOC_ALLOC_SEQ

Monotonic count of successful vmalloc calls this boot (next seq = current value).

VMALLOC_PEAK_PAGES

High-watermark of simultaneously allocated pages (updated on every alloc).

VMALLOC_POLICY_REJECT_COUNT

Counts ZeroSize / policy-limit rejections.

Functions

diag_snapshot

dump_diagnostics

Dump vmalloc diagnostics to the serial console.

dump_live_allocations

Dump all live large allocations with attribution to the serial console.

init

is_live_allocation

Returns whether ptr is currently the base address of a live vmalloc allocation.

last_failure_snapshot

live_allocations_snapshot

Copy live vmalloc allocations into out, in allocation-address order.

vfree

Free a vmalloc allocation.