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

[Yinghai Lu]

On Sat, Jun 30, 2012 at 2:07 AM, Jiang Liu <jiang.liu@xxxxxxxxxx> wrote:
> From: Xishi Qiu <qiuxishi@xxxxxxxxxx>
>
> On architectures with CONFIG_HUGETLB_PAGE_SIZE_VARIABLE set, such as Itanium,
> pageblock_order is a variable with default value of 0. It's set to the right
> value by set_pageblock_order() in function free_area_init_core().
>
> But pageblock_order may be used by sparse_init() before free_area_init_core()
> is called along path:
> sparse_init()
>    ->sparse_early_usemaps_alloc_node()
>        ->usemap_size()
>            ->SECTION_BLOCKFLAGS_BITS
>                ->((1UL << (PFN_SECTION_SHIFT - pageblock_order)) *
> NR_PAGEBLOCK_BITS)
>
> The uninitialized pageblock_size will cause memory wasting because usemap_size()
> returns a much bigger value then it's really needed.
>
> For example, on an Itanium platform,
> sparse_init() pageblock_order=0 usemap_size=24576
> free_area_init_core() before pageblock_order=0, usemap_size=24576
> free_area_init_core() after pageblock_order=12, usemap_size=8
>
> That means 24K memory has been wasted for each section, so fix it by calling
> set_pageblock_order() from sparse_init().
>

can you check attached patch?

That will kill more lines code instead.

Thanks

Yinghai

Attachment: kill_set_pageblock_order.patch
Description: Binary data