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Subject: Re: [PATCH] mm: Introduce GFP_PGTABLE
To:     Matthew Wilcox <willy@infradead.org>,
        Anshuman Khandual <anshuman.khandual@arm.com>
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 <20190112121230.GQ6310@bombadil.infradead.org>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <ddd59fdc-3d8f-4015-e851-e7f099193a1b@c-s.fr>
Date:   Sat, 12 Jan 2019 14:49:29 +0100
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Le 12/01/2019 à 13:12, Matthew Wilcox a écrit :
> On Sat, Jan 12, 2019 at 03:56:38PM +0530, Anshuman Khandual wrote:
>> All architectures have been defining their own PGALLOC_GFP as (GFP_KERNEL |
>> __GFP_ZERO) and using it for allocating page table pages.
> 
> Except that's not true.
> 
>> +++ b/arch/x86/mm/pgtable.c
>> @@ -13,19 +13,17 @@ phys_addr_t physical_mask __ro_after_init = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
>>   EXPORT_SYMBOL(physical_mask);
>>   #endif
>>   
>> -#define PGALLOC_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO)
>> -
>>   #ifdef CONFIG_HIGHPTE
> 
> ...
> 
>>   pte_t *pte_alloc_one_kernel(struct mm_struct *mm)
>>   {
>> -	return (pte_t *)__get_free_page(PGALLOC_GFP & ~__GFP_ACCOUNT);
>> +	return (pte_t *)__get_free_page(GFP_PGTABLE & ~__GFP_ACCOUNT);
>>   }

As far as I can see,

#define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT)

So what's the difference between:

(GFP_KERNEL_ACCOUNT | __GFP_ZERO) & ~__GFP_ACCOUNT

and

(GFP_KERNEL | __GFP_ZERO) & ~__GFP_ACCOUNT

Christophe

> 
> I think x86 was the only odd one out here, but you'll need to try again ...
>