linux-kernel - Re: [PATCH v4 24/36] mm: Remove page fault assumption of compound page size

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Date:   Mon, 25 May 2020 07:59:45 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 24/36] mm: Remove page fault assumption of compound
 page size

On Fri, May 15, 2020 at 06:16:44AM -0700, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> A compound page in the page cache will not necessarily be of PMD size,
> so check explicitly.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  mm/memory.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index f703fe8c8346..d68ce428ddd2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3549,13 +3549,14 @@ static vm_fault_t do_set_pmd(struct vm_fault *vmf, struct page *page)
>  	unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
>  	pmd_t entry;
>  	int i;
> -	vm_fault_t ret;
> +	vm_fault_t ret = VM_FAULT_FALLBACK;
>  
>  	if (!transhuge_vma_suitable(vma, haddr))
> -		return VM_FAULT_FALLBACK;
> +		return ret;
>  
> -	ret = VM_FAULT_FALLBACK;
>  	page = compound_head(page);
> +	if (page_order(page) != HPAGE_PMD_ORDER)
> +		return ret;

Maybe WARN() for page_order(page) > HPAGE_PMD_ORDER. It would be fun to
handle :P
>  
>  	/*
>  	 * Archs like ppc64 need additonal space to store information
> -- 
> 2.26.2
> 

-- 
 Kirill A. Shutemov