linux-kernel - Re: [PATCH 4/6] x86/mem-hotplug: Support initialize page tables bottom up

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Date:	Tue, 24 Sep 2013 08:33:40 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
Cc:	"Rafael J . Wysocki" <rjw@...k.pl>, lenb@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Toshi Kani <toshi.kani@...com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Thomas Renninger <trenn@...e.de>,
	Yinghai Lu <yinghai@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
	mina86@...a86.com, gong.chen@...ux.intel.com,
	vasilis.liaskovitis@...fitbricks.com, lwoodman@...hat.com,
	Rik van Riel <riel@...hat.com>, jweiner@...hat.com,
	prarit@...hat.com, "x86@...nel.org" <x86@...nel.org>,
	linux-doc@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux MM <linux-mm@...ck.org>, linux-acpi@...r.kernel.org,
	imtangchen@...il.com, Zhang Yanfei <zhangyanfei.yes@...il.com>
Subject: Re: [PATCH 4/6] x86/mem-hotplug: Support initialize page tables
 bottom up

Hello,

On Tue, Sep 24, 2013 at 06:08:27PM +0800, Zhang Yanfei wrote:
> +#ifdef CONFIG_MOVABLE_NODE

You don't need the above ifdef.  The compiler will be able to cull the
code as long as memblock_bottom_up() is defined as constant
expression when !MOVABLE_NODE.

> +/**
> + * memory_map_bottom_up - Map [map_start, map_end) bottom up
> + * @map_start: start address of the target memory range
> + * @map_end: end address of the target memory range
> + *
> + * This function will setup direct mapping for memory range [map_start, map_end)
> + * in a heuristic way. In the beginning, step_size is small. The more memory we
> + * map memory in the next loop.

The same comment as before.  Now we have two function with the
identical comment but behaving differently, which isn't nice.

...
> +	 * If the allocation is in bottom-up direction, we start from the
> +	 * bottom and go to the top: first [kernel_end, end) and then
> +	 * [ISA_END_ADDRESS, kernel_end). Otherwise, we start from the top
> +	 * (end of memory) and go to the bottom.
> +	 *
> +	 * The memblock_find_in_range() gets us a block of RAM in
> +	 * [min_pfn_mapped, max_pfn_mapped) used as new pages for page table.
>  	 */
> -	memory_map_top_down(ISA_END_ADDRESS, end);
> +	if (memblock_bottom_up()) {
> +		unsigned long kernel_end;
> +
> +		kernel_end = round_up(__pa_symbol(_end), PMD_SIZE);
> +		memory_map_bottom_up(kernel_end, end);
> +		memory_map_bottom_up(ISA_END_ADDRESS, kernel_end);

Hmm... so, this is kinda weird.  We're doing it in two chunks and
mapping memory between ISA_END_ADDRESS and kernel_end right on top of
ISA_END_ADDRESS?  Can't you give enough information to the mapping
function so that it can map everything on top of kernel_end in single
go?

Thanks.

-- 
tejun
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