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主要还是两个函数free_bootmem_node和free_bootmem

这里主要是标记相应比特位为0，空闲。

/** * free_bootmem_node - mark a page range as usable * @pgdat: node the range resides on * @physaddr: starting address of the range * @size: size of the range in bytes * * Partial pages will be considered reserved and left as they are. * * The range must reside completely on the specified node. */void __init free_bootmem_node(pg_data_t *pgdat, unsigned long physaddr,			      unsigned long size){	unsigned long start, end;	kmemleak_free_part_phys(physaddr, size);	start = PFN_UP(physaddr);	end = PFN_DOWN(physaddr + size);	mark_bootmem_node(pgdat->bdata, start, end, 0, 0);}

/** * free_bootmem - mark a page range as usable * @addr: starting physical address of the range * @size: size of the range in bytes * * Partial pages will be considered reserved and left as they are. * * The range must be contiguous but may span node boundaries. */void __init free_bootmem(unsigned long physaddr, unsigned long size){	unsigned long start, end;	kmemleak_free_part_phys(physaddr, size);	start = PFN_UP(physaddr);	end = PFN_DOWN(physaddr + size);	mark_bootmem(start, end, 0, 0);}

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