linux-kernel - Re: [PATCH 3/6] x86/mm: Factor out of top-down direct mapping setup

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Date:	Tue, 24 Sep 2013 08:27:12 -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 3/6] x86/mm: Factor out of top-down direct mapping setup

On Tue, Sep 24, 2013 at 06:06:41PM +0800, Zhang Yanfei wrote:
> +/**
> + * memory_map_top_down - Map [map_start, map_end) top down
> + * @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 comment reads a bit weird to me.  The step size is increased
gradually but that really isn't really a heuristic and it doesn't
mention mapping direction.

...
> @@ -430,19 +430,13 @@ void __init init_mem_mapping(void)
>  	min_pfn_mapped = real_end >> PAGE_SHIFT;
>  	last_start = start = real_end;
>  
> -	/*
> -	 * We start from the top (end of memory) and go to the bottom.
> -	 * The memblock_find_in_range() gets us a block of RAM from the
> -	 * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
> -	 * for page table.
> -	 */

I think this comment should stay here with the variable names
updated.

> -	while (last_start > ISA_END_ADDRESS) {
> +	while (last_start > map_start) {
>  		if (last_start > step_size) {
>  			start = round_down(last_start - 1, step_size);
> -			if (start < ISA_END_ADDRESS)
> -				start = ISA_END_ADDRESS;
> +			if (start < map_start)
> +				start = map_start;
>  		} else
> -			start = ISA_END_ADDRESS;
> +			start = map_start;
>  		new_mapped_ram_size = init_range_memory_mapping(start,
>  							last_start);
>  		last_start = start;
> @@ -453,8 +447,32 @@ void __init init_mem_mapping(void)
>  		mapped_ram_size += new_mapped_ram_size;
>  	}
>  
> -	if (real_end < end)
> -		init_range_memory_mapping(real_end, end);
> +	if (real_end < map_end)
> +		init_range_memory_mapping(real_end, map_end);
> +}
> +
> +void __init init_mem_mapping(void)
> +{
> +	unsigned long end;
> +
> +	probe_page_size_mask();
> +
> +#ifdef CONFIG_X86_64
> +	end = max_pfn << PAGE_SHIFT;
> +#else
> +	end = max_low_pfn << PAGE_SHIFT;
> +#endif
> +
> +	/* the ISA range is always mapped regardless of memory holes */
> +	init_memory_mapping(0, ISA_END_ADDRESS);
> +
> +	/*
> +	 * We start from the top (end of memory) and go to the bottom.
> +	 * The memblock_find_in_range() gets us a block of RAM from the
> +	 * end of RAM in [min_pfn_mapped, max_pfn_mapped) used as new pages
> +	 * for page table.
> +	 */

And just mention the range and direction in the comment here?

> +	memory_map_top_down(ISA_END_ADDRESS, end);

Thanks.

-- 
tejun
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