Hi all,
When I setup two zones (NORMAL and DMA) in my system, I got the
following wired result from /proc/buddyinfo.
-----------------------------------------------------------------------------------------
root:~> cat /proc/buddyinfo
Node 0, zone DMA 2 1 2 1 1 0 0
1 1 2 2 0 0 0
Node 0, zone Normal 1 1 1 1 1 1 0
0 4294967295 0 4294967295 2 0 0
-----------------------------------------------------------------------------------------
As you see, two area->nr_free went -1.
After dig into the code, I found the problem is in the fun
__free_one_page() when the kernel boot up call free_all_bootmem(). If
two zones setup, it's possible NORMAL zone merged a block whose order
=8 at the first time(this time zone[NORMA]->free_area[8].nr_free = 0)
and found its buddy in the DMA zone. So the two blocks will be merged
and area->nr_free went to -1.