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

On Mon, Jul 2, 2012 at 7:54 PM, Jiang Liu [off-list ref] wrote:

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

quoted

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 =91,=92 or =91;=92 before =91__att=

ribute__=92

quoted

quoted

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 earlyp=

aram.

quoted

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.

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

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.

Thanks

Yinghai

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

On Mon, 2012-07-02 at 20:25 -0700, Yinghai Lu wrote:

quoted

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.

Hrm, HPAGE_SHIFT is initially 0 because we only know at runtime what
huge page sizes are going to be supported (if any).

The business with pageblock_order is new to me and does look bogus today
indeed. But not a huge deal either. Our MAX_ORDER is typically 9 (64K
pages) or 13 (4K pages) and our standard huge page size is generally 16M
so there isn't a big difference here.

Still, maybe something worth looking into...

Cheers,
Ben.

On Tue, 2012-07-03 at 11:29 +0800, Jiang Liu wrote:

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. 

We could split our hugetlbpage_init() into two, with the bit that sets
HPAGE_SHIFT called earlier if it's really an issue.

Cheers,
Ben.