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

Yinghai Lu
2013-05-10T14:57:49Z

On Fri, May 10, 2013 at 3:28 AM, Zhang Yanfei
<zhangyanfei@cn.fujitsu.com> 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@cn.fujitsu.com> 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.

Yinghai