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

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Message-ID: <20190809094406.GA22457@bharath12345-Inspiron-5559>
Date:   Fri, 9 Aug 2019 15:14:06 +0530
From:   Bharath Vedartham <linux.bhar@...il.com>
To:     John Hubbard <jhubbard@...dia.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 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?

Thank you
Bharath
> 
> thanks,
> -- 
> John Hubbard
> NVIDIA