Xen devel - Aug 2009 - difference between DMA heap and dom heap

Hi，all~
I have a question on machine memory. There is pagealloc_keyhandler function
in page_alloc.c file. It has below lines:

    while ( ++zone < NR_ZONES )
    {
        if ( (zone + PAGE_SHIFT) == dma_bitsize )
        {
            printk("    DMA heap: %lukB free\n", total <<
(PAGE_SHIFT-10));
            total = 0;
        }
        if ( (n = avail_heap_pages(zone, zone, -1)) != 0 )
        {
            total += n;
            printk("    heap[%02u]: %lukB free\n", zone, n <<
(PAGE_SHIFT-10));
        }
    }
    printk("    Dom heap: %lukB free\n", total <<
(PAGE_SHIFT-10));


we can see the free space of DMA heap is the sum of free pages from zone[1]
to zone [20], and the dom heap is always 0.
How about DMA heap and Dom heap mean? Why should divide the heap into DMA
heap and Dom heap?

Thanks


Ruby Young


-- 
Best wishes

杨漾
北京航空航天大学计算机学院体系结构研究所
电话:010-82338059-132
邮件:9907yruby@gmail.com
地址：北京市海淀区学院路37号北京航空航天大学新主楼 G座1026
--------------------------------------------------------------------------------
Yang Yang
Institute of Computer Architecture and System
BeiHang University（BUAA）
Tel: (86-10)82338059-132
Email: 9907yruby@gmail.com
Addr: Room 1026,Building G,The New Main Building,37# Xueyuan Rd.,Haidian
District, Beijing 100083, PRC


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