linux-kernel - Re: [PATCH 14/15] mm: Align THP mappings for non-DAX

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Date:   Tue, 1 Oct 2019 13:45:58 +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,
        William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH 14/15] mm: Align THP mappings for non-DAX

On Tue, Sep 24, 2019 at 05:52:13PM -0700, Matthew Wilcox wrote:
> From: William Kucharski <william.kucharski@...cle.com>
> 
> When we have the opportunity to use transparent huge pages to map a
> file, we want to follow the same rules as DAX.
> 
> Signed-off-by: William Kucharski <william.kucharski@...cle.com>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> ---
>  mm/huge_memory.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index cbe7d0619439..670a1780bd2f 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -563,8 +563,6 @@ unsigned long thp_get_unmapped_area(struct file *filp, unsigned long addr,
>  
>  	if (addr)
>  		goto out;
> -	if (!IS_DAX(filp->f_mapping->host) || !IS_ENABLED(CONFIG_FS_DAX_PMD))
> -		goto out;
>  
>  	addr = __thp_get_unmapped_area(filp, len, off, flags, PMD_SIZE);
>  	if (addr)

I think you reducing ASLR without any real indication that THP is relevant
for the VMA. We need to know if any huge page allocation will be
*attempted* for the VMA or the file.

-- 
 Kirill A. Shutemov