Question

调用系统包装函数。

// mpagealloc_64bit.go

func (p *pageAlloc) sysGrow(base, limit uintptr) {

	// Walk up the radix tree and map summaries in as needed.
	for l := range p.summary {
		...
        
		// Map and commit need.
		sysMap(unsafe.Pointer(need.base.addr()), need.size(), p.sysStat)
		sysUsed(unsafe.Pointer(need.base.addr()), need.size())
	}
}

Linux 使用 Huge Page 方式。

Huge Page : 大内存页，相比普通页（4KB）更为高效。

无需交换（swap）。

通过更大页尺寸，减少映射表条目（TLB）。

// mem_linux.go

func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
	p, err := mmap(v, n, _PROT_READ|_PROT_WRITE, _MAP_ANON|_MAP_FIXED|_MAP_PRIVATE, -1, 0)
}

func sysUsed(v unsafe.Pointer, n uintptr) {
	sysHugePage(v, n)
}

func sysHugePage(v unsafe.Pointer, n uintptr) {
	if physHugePageSize != 0 {
        
		beg := alignUp(uintptr(v), physHugePageSize)
		end := alignDown(uintptr(v)+n, physHugePageSize)

		if beg < end {
			madvise(unsafe.Pointer(beg), end-beg, _MADV_HUGEPAGE)
		}
	}
}

Windows 内存分配发生在 sysUsed 调用，以便从堆提取内存（allocSpan）时可以补上已释放内存。

MEM_COMMIT : Allocates memory charges for the specified reserved memory pages.

// mem_windows.go

func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
}

func sysUsed(v unsafe.Pointer, n uintptr) {
	p := stdcall4(_VirtualAlloc, uintptr(v), n, _MEM_COMMIT, _PAGE_READWRITE)
}