Re: [PATCH 4/9] mm/rmap: change hugepage_add_new_anon_rmap to take in a folio

[Sidhartha Kumar]

On 1/20/23 1:17 PM, Matthew Wilcox wrote:
> On Fri, Jan 20, 2023 at 12:45:38PM -0800, Sidhartha Kumar wrote:
> > > > @@ -6176,6 +6186,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> > > >    	spinlock_t *ptl;
> > > >    	int ret = -ENOMEM;
> > > >    	struct page *page;
> > > > +	struct folio *folio = NULL;
> > > >    	int writable;
> > > >    	bool page_in_pagecache = false;
> > > > @@ -6251,12 +6262,15 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
> > > >    		*pagep = NULL;
> > > >    	}
> > > > +	if (page)
> > > > +		folio = page_folio(page);
> > > > +
> > > >    	/*
> > > > -	 * The memory barrier inside __SetPageUptodate makes sure that
> > > > +	 * The memory barrier inside __folio_mark_uptodate makes sure that
> > > >    	 * preceding stores to the page contents become visible before
> > > >    	 * the set_pte_at() write.
> > > >    	 */
> > > > -	__SetPageUptodate(page);
> > > > +	__folio_mark_uptodate(folio);
> >
> > Hi Matthew,
> >
> > In the snippet:
> >
> > page = alloc_huge_page(dst_vma, dst_addr, 0);
> > if (IS_ERR(page)) {
> > 	put_page(*pagep);
> > 	ret = -ENOMEM;
> > 	*pagep = NULL;
> > 	goto out;
> > }
> > copy_user_huge_page(page, *pagep, dst_addr, dst_vma,
> > 		pages_per_huge_page(h));
> >
> > I thought the IS_ERR() call does not handle the NULL case and is a check for
> > high memory addresses, and copy_user_huge_page() path does not seem to
> > handle the NULL case as well but alloc_huge_page() can possibly return NULL
> > so I was unsure about how to handle the folio conversion.
>
> I'm not sure how alloc_huge_page() can return NULL.  It seems like it
> returns ERR_PTR(-ENOSPC) or ERR_PTR(-ENOMEM) if it cannot allocate memory?
I see now, I agree that page cannot be NULL at the return from 
alloc_huge_page, I will make that change in v2.

Thanks,
Sidhartha Kumar