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

[Tang Chen]

On 09/03/2013 10:48 AM, Yinghai Lu wrote:
> On Mon, Sep 2, 2013 at 6:06 PM, Tang Chen<tangchen@xxxxxxxxxxxxxx>  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.
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