linux-kernel - Re: [PATCH] mm: Introduce GFP

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Date:   Sat, 12 Jan 2019 14:49:29 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Matthew Wilcox <willy@...radead.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     mark.rutland@....com, mhocko@...e.com, linux-sh@...r.kernel.org,
        peterz@...radead.org, catalin.marinas@....com,
        dave.hansen@...ux.intel.com, will.deacon@....com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kvmarm@...ts.cs.columbia.edu, linux@...linux.org.uk,
        mingo@...hat.com, vbabka@...e.cz, rientjes@...gle.com,
        marc.zyngier@....com, rppt@...ux.vnet.ibm.com, shakeelb@...gle.com,
        kirill@...temov.name, tglx@...utronix.de,
        linux-arm-kernel@...ts.infradead.org, ard.biesheuvel@...aro.org,
        robin.murphy@....com, steve.capper@....com,
        christoffer.dall@....com, james.morse@....com,
        aneesh.kumar@...ux.ibm.com, akpm@...ux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] mm: Introduce GFP_PGTABLE



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 ...
>