memblock:What is the difference between memory and physmem?

struct memblock {
bool bottom_up; /* is bottom up direction? */
phys_addr_t current_limit;
struct memblock_type memory;
struct memblock_type reserved;
#ifdef CONFIG_HAVE_MEMBLOCK_PHYS_MAP
struct memblock_type physmem;
#endif
};
What is the difference between memory and physmem?

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I have seen the difference between memory and physics. Help me expand my knowledge and learn many things.
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