linux-kernel - Re: [PATCH v5 4/6] x86/mem-hotplug: Support initialize page tables in bottom-up

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Message-ID: <52445606.7030108@gmail.com>
Date:	Thu, 26 Sep 2013 23:43:02 +0800
From:	Zhang Yanfei <zhangyanfei.yes@...il.com>
To:	Tejun Heo <tj@...nel.org>
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@...fujitsu.com>
Subject: Re: [PATCH v5 4/6] x86/mem-hotplug: Support initialize page tables
 in bottom-up

Hello tejun,

On 09/26/2013 10:48 PM, Tejun Heo wrote:
> Hello,
> 
> On Wed, Sep 25, 2013 at 02:30:51AM +0800, Zhang Yanfei wrote:
>> +/**
>> + * 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 bottom-up.
> 
> Ditto about the comment.

OK, will do.

> 
>> + */
>> +static void __init memory_map_bottom_up(unsigned long map_start,
>> +					unsigned long map_end)
>> +{
>> +	unsigned long next, new_mapped_ram_size, start;
>> +	unsigned long mapped_ram_size = 0;
>> +	/* step_size need to be small so pgt_buf from BRK could cover it */
>> +	unsigned long step_size = PMD_SIZE;
>> +
>> +	start = map_start;
>> +	min_pfn_mapped = start >> PAGE_SHIFT;
>> +
>> +	/*
>> +	 * We start from the bottom (@map_start) and go to the top (@map_end).
>> +	 * 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.
>> +	 */
>> +	while (start < map_end) {
>> +		if (map_end - start > step_size) {
>> +			next = round_up(start + 1, step_size);
>> +			if (next > map_end)
>> +				next = map_end;
>> +		} else
>> +			next = map_end;
>> +
>> +		new_mapped_ram_size = init_range_memory_mapping(start, next);
>> +		start = next;
>> +
>> +		if (new_mapped_ram_size > mapped_ram_size)
>> +			step_size <<= STEP_SIZE_SHIFT;
>> +		mapped_ram_size += new_mapped_ram_size;
>> +	}
>> +}
> 
> As Yinghai pointed out in another thread, do we need to worry about
> falling back to top-down?

I've explained to him. Nop, we don't need to worry about that. Because even
the min_pfn_mapped becomes ISA_END_ADDRESS in the second call below, we won't
allocate memory below the kernel because we have limited the allocation above
the kernel.

Thanks.

-- 
Thanks.
Zhang Yanfei
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