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

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Message-ID: <CAE9FiQWzfLkeQs8O22MUEmuGUx=jPi5s=wZt2fcpFMcwrzt3uA@mail.gmail.com>
Date:	Sat, 30 Jun 2012 13:15:46 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Jiang Liu <jiang.liu@...wei.com>
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

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

Download attachment "kill_set_pageblock_order.patch" of type "application/octet-stream" (2426 bytes)