Re: [PATCH] mm: setup pageblock_order before it's used by sparse

On 2012-7-3 4:43, Yinghai Lu wrote:

On Sun, Jul 1, 2012 at 7:01 PM, Jiang Liu [off-list ref] wrote:

quoted

Hi Yinghai,
        The patch fails compilation as below:
mm/page_alloc.c:151: error: initializer element is not constant
mm/page_alloc.c:151: error: expected ?,? or ?;? before ?__attribute__?

On IA64, HUGETLB_PAGE_ORDER has dependency on variable hpage_shift.
# define HUGETLB_PAGE_ORDER        (HPAGE_SHIFT - PAGE_SHIFT)
# define HPAGE_SHIFT               hpage_shift

And hpage_shift could be changed by early parameter "hugepagesz".
So seems will still need to keep function set_pageblock_order().

ah,  then use use _DEFAULT instead and later could update that in earlyparam.

So attached -v2 should  work.

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.

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

Thanks!
Gerry

Thanks

Yinghai

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>