Re: [PATCH RESEND 2/3] x86, mm: Update min_pfn_mapped in add_pfn_range_mapped().

Tang Chen
2013-09-03T05:39:40Z

On 09/03/2013 10:48 AM, Yinghai Lu wrote:
> On Mon, Sep 2, 2013 at 6:06 PM, Tang Chen<tangchen@cn.fujitsu.com> wrote:
>> Hi Yinghai,
>>
>> On 09/03/2013 02:41 AM, Yinghai Lu wrote:
>
>> How about change the "for (from low to high)" in init_range_memory_mapping()
>> to
>> "for_rev(from high to low)" ?
>> Then we can update min_pfn_mapped in add_pfn_range_mapped().
>>
>> And also, the outer loop is from high to low, we can change the inner loop
>> to be from high
>> to low too.
>
> No. there is other reason for doing local from low to high.
>
> kernel_physical_mapping_init() could clear some mapping near the end
> of PUG/PMD entries but not the head.

Thanks for your explanation. But sorry, I'd like to understand it more
clearly.

Are you talking about the following code ?
phys_pud_init()
{
if (addr >= end) {
if (!after_bootmem &&
!e820_any_mapped(addr & PUD_MASK, next,
E820_RAM) &&
!e820_any_mapped(addr & PUD_MASK, next,
E820_RESERVED_KERN))
set_pud(pud, __pud(0));
continue;
}
}
It will clear the PUD/PMD out of range.

But,
init_mem_mapping()
{
while (from high to low) {
init_range_memory_mapping()
{
for (from low to high) { /* I'm saying changing this
loop */
init_memory_mapping()
{
for () { /* Not this one */
kernel_physical_mapping_init();
}
add_pfn_range_mapped();
}
}
}
}
}

I'm saying changing the outer loop in init_range_memory_mapping(), not
the one in init_memory_mapping().
I think it is OK to call init_memory_mapping() with any order. The loop
is out of init_memory_mapping(), right ?

In init_memory_mapping(), it is still from low to high. But when the
kernel_physical_mapping_init() finished,
we can update min_pfn_mapped in add_pfn_range_mapped() because the outer
loop is from high to low.

Am I missing something here ? Please tell me.

>
>>
>> I think updating min_pfn_mapped in init_mem_mapping() is less readable. And
>> min_pfn_mapped
>> and max_pfn_mapped should be updated together.
>
> min_pfn_mapped is early local variable to control allocation in alloc_low_pages.
> put it in init_mem_mapping is more readable.
>

But add_pfn_range_mapped() is in the same file with init_mem_mapping().
I think
it is OK to update min_pfn_mapped in it.

Thanks.