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

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Message-ID: <4FF100F0.9050501@huawei.com>
Date:	Mon, 2 Jul 2012 10:01:20 +0800
From:	Jiang Liu <jiang.liu@...wei.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Tony Luck <tony.luck@...el.com>,
	Xishi Qiu <qiuxishi@...wei.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>,
	Keping Chen <chenkeping@...wei.com>, <linux-mm@...ck.org>,
	<stable@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Jiang Liu <liuj97@...il.com>
Subject: Re: [PATCH] mm: setup pageblock_order before it's used by sparse

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().

Thanks!
Gerry

On 2012-7-1 4:15, Yinghai Lu wrote:
> On Sat, Jun 30, 2012 at 2:07 AM, Jiang Liu <jiang.liu@...wei.com> wrote:
>> From: Xishi Qiu <qiuxishi@...wei.com>
>>
>> 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


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