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Date: Mon, 22 Apr 2013 17:46:50 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Subject: Re: [PATCH -V6 17/27] mm/THP: Add pmd args to pgtable deposit and
 withdraw APIs
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On Mon, Apr 22, 2013 at 03:30:51PM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
> 
> This will be later used by powerpc THP support. In powerpc we want to use
> pgtable for storing the hash index values. So instead of adding them to
> mm_context list, we would like to store them in the second half of pmd
> 
> Cc: Andrea Arcangeli <aarcange@redhat.com>

*snip*

>  #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -void pgtable_trans_huge_deposit(struct mm_struct *mm, pgtable_t pgtable)
> +void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
> +				pgtable_t pgtable)
>  {
>  	assert_spin_locked(&mm->page_table_lock);
>  
> @@ -141,7 +142,7 @@ void pgtable_trans_huge_deposit(struct mm_struct *mm, pgtable_t pgtable)
>  #ifndef __HAVE_ARCH_PGTABLE_WITHDRAW
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  /* no "address" argument so destroys page coloring of some arch */
> -pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm)
> +pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp)
>  {
>  	pgtable_t pgtable;

This will add micro overhead with more variables put in certain regs
or stack. The micro overhead could be optimized away by wrapping the
call with a generic and per-arch header and by adding a __ prefix to
the above one in the generic .c file. I'm neutral but I pointed out so
others are free to comment on it.

Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>