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

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Message-ID: <52419264.3020409@gmail.com>
Date:	Tue, 24 Sep 2013 21:23:48 +0800
From:	Zhang Yanfei <zhangyanfei.yes@...il.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	"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
Subject: Re: [PATCH 4/6] x86/mem-hotplug: Support initialize page tables bottom
 up

On 09/24/2013 08:33 PM, Tejun Heo wrote:
> 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.

yeah, will remove the #if. thanks.

> 
>> +/**
>> + * 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.

OK, will change them.

> 
> ...
>> +	 * 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?

You mean we should call memory_map_bottom_up like this:

memory_map_bottom_up(ISA_END_ADDRESS, end)

right?

> 
> Thanks.
> 


-- 
Thanks.
Zhang Yanfei
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