Re: question about memory-hotplug

[tgh <tianguanhua@ncic.ac.cn>]

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Thank you for your reply

Thank you


Yasunori Goto 写道:
>>> Yes there are. Zone is still necessary for page reclaim.
>>> Node and zonelist are used for NUMA system.
>>>   
>>>       
>> Buddy allocate memory with the mem_section[] and without  zone-aware 
>> ,while it reclaim memory with zone,is it right?
>> I am confused about the functions of the zone and node in the system 
>> ,when the sparsemem is on
>>     
>
> Basically, mem_section[] is for pointer to mem_map.
> It doesn't count how many pages are allocated/freed in its section. 
> This just divides mem_map[] as discontiguous.
>
> Buddy allocater must know 2 things. 
>
> First is the address of buddy page against target page.
> It can be calculated as --relative offset-- from target page.
> (See: __page_find_buddy()). So, buddy allocater doesn't know mem_map is 
> discontigous or not.
> From this view point, Buddy allocater doen't concern about any
> zone, node, nor mem_section.
>
> Second is free_list for managing free pages. Its list is connected
> to zone. So, buddy allocator must know about only zone's address
> and target page's address. It doesn't know mem_map is contiguous
> or not too.
>
> Current zone is used for manage freed/active/inactive pages.
> Zone has link lists and counters of their pages.
> There is no assumption that zone is contiguous from this view point.
> Even if there is a memory hole in zone, zone can work.
>
> Just memmap array has assumption that physicall memory is contigous.
> Index of memmap is decided by Page Frame Number. If there is big
> memory hole in memory, many space of it will be wasted.
> This is why mem_section is used for sparse mem.
>
> Node is for NUMA node now. Each node have each pgdat. This is
> unit for managing memory areas which has different access
> speed. Kernel can use nearest memory from cpu by finding appropriate
> pgdat. 
>
> Old DISCONTIG_MEM defines one pgdat for one contigous memory area.
> But many people dislike now. If system has too much memory area 
> which area is small size, too much pgdats and big zonelists
> are big cause of system load.
>
>
> Bye.
>
>   


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