quoted

Hi Yinghai,

I'm afraid the v2 will break powerpc. Currently only IA64 and PowerPC
supports variable hugetlb size.

HPAGE_SHIFT is a variable default to 0 on powerpc. But seems PowerPC
is doing something wrong here, according to it's mm initialization
sequence as below:
start_kernel()
        setup_arch()
                paging_init()
                        free_area_init_node()
                                set_pageblock_order()
                                        refer to HPAGE_SHIFT (still 0)
        init_rest()
                do_initcalls()
                        hugetlbpage_init()
                                setup HPAGE_SHIFT
That means pageblock_order is always set to "MAX_ORDER - 1", not sure
whether this is intended. And it has the same issue as IA64 of wasting
memory if CONFIG_SPARSE is enabled.

adding BenH, need to know if it is powerpc intended.

quoted

So it would be better to keep function set_pageblock_order(), it will
fix the memory wasting on both IA64 and PowerPC.

Should setup pageblock_order as early as possible to avoid confusing.

OK, waiting response from PPC. If we could find some ways to set HPAGE_SIZE
early on PPC too, we can setup pageblock_order in arch instead of page_alloc.c
as early as possible.

Thanks!
Gerry