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Re: [PATCH 04/11] ARCv2: mm: THP support

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  Re: [PATCH 04/11] ARCv2: mm: THP support "Kirill A. Shutemov" <kirill@shutemov.name> - 2015-08-27 17:40 +0200
    Re: [PATCH 04/11] ARCv2: mm: THP support Vineet Gupta <vgupta@synopsys.com> - 2015-08-27 19:00 +0200

#1214656 — Re: [PATCH 04/11] ARCv2: mm: THP support

On Thu, Aug 27, 2015 at 02:33:07PM +0530, Vineet Gupta wrote:
> +pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
> +{
> +	struct list_head *lh;
> +	pgtable_t pgtable;
> +	pte_t *ptep;
> +
> +	assert_spin_locked(&mm->page_table_lock);
> +
> +	pgtable = pmd_huge_pte(mm, pmdp);
> +	lh = (struct list_head *) pgtable;
> +	if (list_empty(lh))
> +		pmd_huge_pte(mm, pmdp) = (pgtable_t) NULL;
> +	else {
> +		pmd_huge_pte(mm, pmdp) = (pgtable_t) lh->next;
> +		list_del(lh);
> +	}

Side question: why pgtable_t is unsigned long on ARC and not struct page *
or pte_t *, like on other archs? We could avoid these casts.

-- 
 Kirill A. Shutemov
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#1214702

On Thursday 27 August 2015 09:02 PM, Kirill A. Shutemov wrote:
> On Thu, Aug 27, 2015 at 02:33:07PM +0530, Vineet Gupta wrote:
>> > +pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
>> > +{
>> > +	struct list_head *lh;
>> > +	pgtable_t pgtable;
>> > +	pte_t *ptep;
>> > +
>> > +	assert_spin_locked(&mm->page_table_lock);
>> > +
>> > +	pgtable = pmd_huge_pte(mm, pmdp);
>> > +	lh = (struct list_head *) pgtable;
>> > +	if (list_empty(lh))
>> > +		pmd_huge_pte(mm, pmdp) = (pgtable_t) NULL;
>> > +	else {
>> > +		pmd_huge_pte(mm, pmdp) = (pgtable_t) lh->next;
>> > +		list_del(lh);
>> > +	}
> Side question: why pgtable_t is unsigned long on ARC and not struct page *
> or pte_t *, like on other archs? We could avoid these casts.

This goes back how I did this for ARC long back to avoid page_address() calls in
general case. e.g. pte_alloc_one(), pmd_populate(), pte_free()... all needed to
convert struct page to unsigned long. It was micro-optimization of sorts, but
served us well.

I could perhaps see try making it pte *, that will certainly remove a bunch of
other casts as well.

-Vineet


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