linux-kernel - Re: [PATCH 4/9] mm/rmap: change hugepage_add_new_anon

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Message-ID: <Y8ot5Y01TWmB4sBj@casper.infradead.org>
Date:   Fri, 20 Jan 2023 06:00:05 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, songmuchun@...edance.com,
        mike.kravetz@...cle.com, jhubbard@...dia.com
Subject: Re: [PATCH 4/9] mm/rmap: change hugepage_add_new_anon_rmap to take
 in a folio

On Thu, Jan 19, 2023 at 01:14:41PM -0800, Sidhartha Kumar wrote:
> @@ -5599,9 +5603,9 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>  		goto out_release_all;
>  	}
>  
> -	copy_user_huge_page(new_page, old_page, address, vma,
> +	copy_user_huge_page(&new_folio->page, old_page, address, vma,
>  			    pages_per_huge_page(h));

We have a folio_copy(), but it feels to me like we need a
folio_copy_user() so that we can use copy_user_page() on machines
with virtual caches.

> @@ -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);

I suggest that "page" can never be NULL or __SetPageUptodate() would
have crashed.