Question

直接从堆提取一个大小合适的内存块。

// malloc.go

func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {    
    var s *mspan
    
    if size <= maxSmallSize {
        // 小对象 ...
    } else {
        // 大对象 ...
        s = largeAlloc(size, needzero, noscan)
    }
    
    return x
}

func largeAlloc(size uintptr, needzero bool, noscan bool) *mspan {
    
    // 大块内存以页为单位。
    npages := size >> _PageShift
    if size & _PageMask != 0 {
        npages++
    }
    
    // 直接从堆分配。
    spc := makeSpanClass(0, noscan)
    s := mheap_.alloc(npages, spc, needzero)
    
    // 放到 central 管理列表。
    if go115NewMCentralImpl {
		// Put the large span in the mcentral swept list so that it's
		// visible to the background sweeper.
        mheap_.central[spc].mcentral.fullSwept(mheap_.sweepgen).push(s)
    }
    
    return s
}