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Subject: Re: [Linux-kernel-mentees][PATCH v4 1/1] sgi-gru: Remove *pte_lookup
 functions
To:     Bharath Vedartham <linux.bhar@gmail.com>, <arnd@arndb.de>,
        <gregkh@linuxfoundation.org>, <sivanich@sgi.com>
CC:     <ira.weiny@intel.com>, <jglisse@redhat.com>,
        <william.kucharski@oracle.com>, <hch@lst.de>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <linux-kernel-mentees@lists.linuxfoundation.org>
References: <1565290555-14126-1-git-send-email-linux.bhar@gmail.com>
 <1565290555-14126-2-git-send-email-linux.bhar@gmail.com>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <b659042a-f2c3-df3c-4182-bb7dd5156bc1@nvidia.com>
Date:   Thu, 8 Aug 2019 16:21:44 -0700
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On 8/8/19 11:55 AM, Bharath Vedartham wrote:
...
>  static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  		    int write, int atomic, unsigned long *gpa, int *pageshift)
>  {
>  	struct mm_struct *mm = gts->ts_mm;
>  	struct vm_area_struct *vma;
>  	unsigned long paddr;
> -	int ret, ps;
> +	int ret;
> +	struct page *page;
>  
>  	vma = find_vma(mm, vaddr);
>  	if (!vma)
> @@ -263,21 +187,33 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
>  
>  	/*
>  	 * Atomic lookup is faster & usually works even if called in non-atomic
> -	 * context.
> +	 * context. get_user_pages_fast does atomic lookup before falling back to
> +	 * slow gup.
>  	 */
>  	rmb();	/* Must/check ms_range_active before loading PTEs */
> -	ret = atomic_pte_lookup(vma, vaddr, write, &paddr, &ps);
> -	if (ret) {
> -		if (atomic)
> +	if (atomic) {
> +		ret = __get_user_pages_fast(vaddr, 1, write, &page);
> +		if (!ret)
>  			goto upm;
> -		if (non_atomic_pte_lookup(vma, vaddr, write, &paddr, &ps))
> +	} else {
> +		ret = get_user_pages_fast(vaddr, 1, write ? FOLL_WRITE : 0, &page);
> +		if (!ret)
>  			goto inval;
>  	}
> +
> +	paddr = page_to_phys(page);
> +	put_user_page(page);
> +
> +	if (unlikely(is_vm_hugetlb_page(vma)))
> +		*pageshift = HPAGE_SHIFT;
> +	else
> +		*pageshift = PAGE_SHIFT;
> +
>  	if (is_gru_paddr(paddr))
>  		goto inval;
> -	paddr = paddr & ~((1UL << ps) - 1);
> +	paddr = paddr & ~((1UL << *pageshift) - 1);
>  	*gpa = uv_soc_phys_ram_to_gpa(paddr);
> -	*pageshift = ps;

Why are you no longer setting *pageshift? There are a couple of callers
that both use this variable.


thanks,
-- 
John Hubbard
NVIDIA