分配一個新的線性區

do_mmap
    =>ret = do_mmap_pgoff(file, addr, len, prot, flag, offset >> PAGE_SHIFT);
        =>len = PAGE_ALIGN(len);
        =>addr = get_unmapped_area(file, addr, len, pgoff, flags);//找到一個空閒的線性區
            =>get_area = current->mm->get_unmapped_area;
            =>addr = get_area(file, addr, len, pgoff, flags);//mm
 
->get_unmapped_area = arch_get_unmapped_area;
                =>addr = PAGE_ALIGN(addr);
                =>vma = find_vma(mm, addr);
                    =>注意，vma && vma->vm_end > addr 的優先順序是 > 更高，可以理解成 (vma && (vma->vm_end > addr))
                    =>通過紅黑樹查詢
 
                full_search://for迴圈的含義：探測找到空閒並且滿足大小的空間，用於後續分配新的vma
                    for (vma = find_vma(mm, addr); ; vma = vma->vm_next)
                        if (!vma || addr + len <= vma->vm_start)//到vma連結串列尾部或者在連結串列找到合適的空位置，參考文章《記憶體學習3 vma研究》http://mp.blog.csdn.net/mdeditor/index/79157302
                            mm->free_area_cache = addr + len;
                            return addr;
                        addr = vma->vm_end;//這個addr不合適，挪一個位置繼續探測
        =>error = security_file_mmap(file, reqprot, prot, flags, addr, 0
 
);
            =>security_ops->file_mmap (file, reqprot, prot, flags, addr, addr_only);        
        =>mmap_region(file, addr, len, flags, vm_flags, pgoff, accountable);
            =>vma = find_vma_prepare(mm, addr, &prev, &rb_link, &rb_parent);
            =>vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);//真正分配vma的地方
            vma->vm_mm = mm;
            vma->vm_start = addr;
            vma->vm_end = addr + len;
            vma->vm_flags = vm_flags;
            vma->vm_page_prot = protection_map[vm_flags &
                        (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
            vma->vm_pgoff = pgoff;
            =>if (file)
                vma->vm_file = file;
                get_file(file);
                error = file->f_op->mmap(file, vma);
            =>addr = vma->vm_start;
            pgoff = vma->vm_pgoff;
            vm_flags = vma->vm_flags;
            =>vma_link(mm, vma, prev, rb_link, rb_parent);//將新的vma加入連結串列和紅黑樹裡面，裡面很複雜，可以牽出一頭牛
            =>if (vm_flags & VM_LOCKED)//如果不鎖存的話屆時缺頁中斷分配頁框和重新整理頁表
                mm->locked_vm += len >> PAGE_SHIFT;
                make_pages_present(addr, addr + len);//分配頁框和重新整理頁表
                    =>vma = find_vma(current->mm, addr);
                    =>ret = get_user_pages(current, current->mm, addr, len, write, 0, NULL, NULL);

分配了線性區之後只是空頭支票，沒有乾貨，當訪問記憶體的時候的時候要走入缺頁中斷
另外一個與分配線性區類似的是malloc，呼叫do_brk

do_brk
    =>if (security_vm_enough_memory(len >> PAGE_SHIFT)) //len >> PAGE_SHIFT 把len轉換成pages作為引數，
        =>security_ops->vm_enough_memory(current->mm, pages);
            =>selinux_vm_enough_memory
                =>__vm_enough_memory//判斷實體記憶體是否夠用，是否能申請下len大小的空間，這個函式貌似很有用，後續好好研究一下
    =>vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
    =>vma->vm_mm = mm;
    vma->vm_start = addr;
    vma->vm_end = addr + len;
    vma->vm_pgoff = pgoff;
    vma->vm_flags = flags;
    vma->vm_page_prot = protection_map[flags & (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
    =>vma_link(mm, vma, prev, rb_link, rb_parent);
    =>make_pages_present(addr, addr + len);