Subject: [PATCH] arm64:mm: free the useless initial page table

From: [email-masked] (zhichang.yuan)
Date: Tue, 25 Nov 2014 22:41:35 +0800

On 2014?11?24? 22:32, Catalin Marinas wrote:
> On Fri, Nov 21, 2014 at 08:27:40AM +0000, zhichang.yuan at linaro.org wrote:
>> From: "zhichang.yuan" <[email-masked]>
>>
>> For 64K page system, after mapping a PMD section, the corresponding initial
>> page table is not needed any more. That page can be freed.
>>
>> Signed-off-by: Zhichang Yuan <[email-masked]>
>> ---
>>  arch/arm64/mm/mmu.c |    5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index f4f8b50..12a336b 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -191,8 +191,11 @@ static void __init alloc_init_pmd(pud_t *pud, unsigned long addr,
>>  			 * Check for previous table entries created during
>>  			 * boot (__create_page_tables) and flush them.
>>  			 */
>> -			if (!pmd_none(old_pmd))
>> +			if (!pmd_none(old_pmd)) {
>>  				flush_tlb_all();
>> +				if (pmd_table(old_pmd))
>> +					memblock_free(pte_pfn(pmd_pte(old_pmd)) << PAGE_SHIFT, PAGE_SIZE);
>> +			}
> For consistency with alloc_init_pud(), could you do:
>
> 	phys_addr_t table = __pa(pte_offset(&old_pmd, 0));
> 	memblock_free(table, PAGE_SIZE);
Just as Laura comments, the pte_offset will convert the PA to VA, and then convert  VA to PA. It seems to be
verbose. That is why i use pte_pfn. Anyway, the consistency is better, i will revise it.

> Since you are at this, for alloc_init_pud() could you please move the
> flush_tlb_all() before memblock_free()? Theoretical problem really but
> it's nice for consistency.
>
> Thanks.
>
As for this issue, i have a small question.  Since the new PMD entry had been set by set_pmd, why not do the
tlb flush as soon as we can?

Thanks!