Re: [PATCH] x86: mm: Remove unnecessary assignment for max_pfn_mapped

[Zhang Yanfei]

于 2013年05月10日 22:57, Yinghai Lu 写道:
> On Fri, May 10, 2013 at 3:28 AM, Zhang Yanfei
> <zhangyanfei@xxxxxxxxxxxxxx> wrote:
>> 于 2013年05月10日 17:27, Yinghai Lu 写道:
>>> On Fri, May 10, 2013 at 2:01 AM, Zhang Yanfei
>>> <zhangyanfei@xxxxxxxxxxxxxx> wrote:
>>>> init_memory_mapping will set max_pfn_mapped:
>>>> int_memory_mapping
>>>>   --> add_pfn_range_mapped
>>>>     --> max_pfn_mapped = max(max_pfn_mapped, end_pfn)
>>>>
>>>> In init_mem_mapping, before we set max_pfn_mapped to 0, we
>>>> have already called init_memory_mapping to setup pagetable
>>>> for [0, ISA_END_ADDRESS], and that sets max_pfn_mapped. So
>>>> the assignment to 0 is not necessary, remove it.
>>>
>>> NAK.
>>>
>>> for 32bit or Xen, max_pfn_mapped is set way before in head_32.S and
>>> xen-enlighen.
>>
>> Hi Yinghai
>>
>> I might be wrong, but just from the code in init_mem_mapping only:
>>
>>  410         /* the ISA range is always mapped regardless of memory holes */
>>  411         init_memory_mapping(0, ISA_END_ADDRESS);
>>  412
>>  413         /* xen has big range in reserved near end of ram, skip it at first.*/
>>  414         addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE, PMD_SIZE);
>>  415         real_end = addr + PMD_SIZE;
>>  416
>>  417         /* step_size need to be small so pgt_buf from BRK could cover it */
>>  418         step_size = PMD_SIZE;
>>  419         max_pfn_mapped = 0; /* will get exact value next */
>>
>> Line 411 set max_pfn_mapped, and then line 419 set it to zero again, so
>> why keep the later assignment?
> 
> the comment says: /* will get exact value next */
> 
> For x86 32bit path, and xen set bigger max_pfn_mapped before.
> 

Hello Yinghai,

I kindly understand what you mean now. But I think we can put the reset of
max_pfn_mapped at the beginning of init_mem_mapping. That looks more logical.

See patch below, please.

Thanks
Zhang

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