linux-kernel - Re: [PATCH v3 15/44] metag: Huge TLB

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Date:	Fri, 11 Jan 2013 09:58:34 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
CC:	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 15/44] metag: Huge TLB

On 10/01/13 16:57, Dave Hansen wrote:
> On 01/10/2013 07:30 AM, James Hogan wrote:
>> +pte_t *huge_pte_alloc(struct mm_struct *mm,
>> +			unsigned long addr, unsigned long sz)
>> +{
>> +	pgd_t *pgd;
>> +	pud_t *pud;
>> +	pmd_t *pmd;
>> +	pte_t *pte;
>> +
>> +	pgd = pgd_offset(mm, addr);
>> +	pud = pud_offset(pgd, addr);
>> +	pmd = pmd_offset(pud, addr);
>> +	pte = pte_alloc_map(mm, NULL, pmd, addr);
>> +	pgd->pgd &= ~_PAGE_SZ_MASK;
>> +	pgd->pgd |= _PAGE_SZHUGE;
>> +
>> +	return pte;
>> +}
> 
> I'd be a bit surprised if you don't have to check for NULL during the
> walk down the page tables.  Is there a special reason on your
> architecture that this is unnecessary?
> 
> (There are several of these, not just this one).
> 

Meta only has 2 levels of page tables which map to the linux levels.
asm/pgtable.h includes asm-generic/pgtable-nopmd.h, which includes
asm-generic/pgtable-nopud.h, so the pmd and pud levels get folded into
the pgd.

Cheers
James

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