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

Yinghai Lu
2013-09-03T06:34:55Z

On Mon, Sep 2, 2013 at 10:38 PM, Tang Chen <tangchen@cn.fujitsu.com> wrote:
> 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.

Yes, that looks ok,

but will make the code more hard to understand, aka more dependency.

the only purpose for min_pfn_mapped is for control allocation for
alloc_low_pages.

so put it's updating in init_mem_mapping is clear and less twisting.

also in my patchset that put page table in local node, min_pfn_mapped
is replaced by
local_min_pfn_mapped per node.

Yinghai