On 2/18/2010 6:00 PM, KAMEZAWA Hiroyuki wrote:
memmap for memory holes should be marked as PG_reserved and never be freed by free_bootmem(). Then, memmap for memory holes will not be in buddy allocator. Again, pfn_valid() just show "there is memmap", not for "there is a valid page"
ARM seems to have been freeing the memmap holes for a long time. I'm pretty sure there would be a lot of pushback if we tried to change that. For example, in my memory map running FLATMEM, I would be consuming an extra ~7 MB of memory if these structures were not freed.
As a compromise, perhaps we could free everything except the first 'pageblock_nr_pages' in a hole? This would guarantee that move_freepages() doesn't deference any memory that doesn't belong to the memmap -- but still only waste a relatively small amount of memory. For a 4 MB page block, it should only consume an extra 32 KB per hole in the memory map.
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