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

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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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