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

Zhang Yanfei
2013-05-10T10:30:25Z

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?

Thanks
Zhang