linux-kernel - Re: [Linux-kernel-mentees][PATCH v4 1/1] sgi-gru: Remove *pte

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Message-ID: <f2f928f1-2747-e693-1a7f-14ad5f57fef5@nvidia.com>
Date:   Fri, 9 Aug 2019 11:03:14 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Bharath Vedartham <linux.bhar@...il.com>
CC:     <arnd@...db.de>, <gregkh@...uxfoundation.org>, <sivanich@....com>,
        <ira.weiny@...el.com>, <jglisse@...hat.com>,
        <william.kucharski@...cle.com>, <hch@....de>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-kernel-mentees@...ts.linuxfoundation.org>
Subject: Re: [Linux-kernel-mentees][PATCH v4 1/1] sgi-gru: Remove *pte_lookup
 functions

On 8/9/19 2:44 AM, Bharath Vedartham wrote:
> On Thu, Aug 08, 2019 at 04:21:44PM -0700, John Hubbard wrote:
>> 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.
> Hi John,
> 
> I did set *pageshift. The if statement above sets *pageshift. ps was
> used to retrive the pageshift value when the pte_lookup functions were
> present. ps was passed by reference to those functions and set by them.
> But here since we are trying to remove those functions, we don't need ps
> and we directly set *pageshift to HPAGE_SHIFT or PAGE_SHIFT based on the
> type of vma.
> 
> Hope this clears things up?
> 

Right you are, sorry for overlooking that. Looks good.

thanks,
-- 
John Hubbard
NVIDIA