linux-kernel - Re: [PATCH] mm: khugepaged: skip huge page collapse for special files

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Date:   Wed, 27 Oct 2021 21:50:24 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Yang Shi <shy828301@...il.com>
Cc:     hughd@...gle.com, sunhao.th@...il.com,
        kirill.shutemov@...ux.intel.com, songliubraving@...com,
        andrea.righi@...onical.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] mm: khugepaged: skip huge page collapse for special files

On Wed, Oct 27, 2021 at 12:52:21PM -0700, Yang Shi wrote:
> +++ b/mm/khugepaged.c
> @@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
>  	if (!transhuge_vma_enabled(vma, vm_flags))
>  		return false;
>  
> -	/* Enabled via shmem mount options or sysfs settings. */
> -	if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
> +	if (vma->vm_file)
>  		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
>  				HPAGE_PMD_NR);
> -	}
> +
> +	/* Enabled via shmem mount options or sysfs settings. */
> +	if (shmem_file(vma->vm_file))
> +		return shmem_huge_enabled(vma);

This doesn't make sense to me.  if vma->vm_file, we already returned,
so this is dead code.

>  	/* THP settings require madvise. */
>  	if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
>  		return false;
>  
> -	/* Read-only file mappings need to be aligned for THP to work. */
> +	/* Only regular file is valid */
>  	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
> -	    !inode_is_open_for_write(vma->vm_file->f_inode) &&
>  	    (vm_flags & VM_EXEC)) {
> -		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
> -				HPAGE_PMD_NR);
> +		struct inode *inode = vma->vm_file->f_inode;
> +
> +		return !inode_is_open_for_write(inode) &&
> +			S_ISREG(inode->i_mode);
>  	}
>  
>  	if (!vma->anon_vma || vma->vm_ops)
> -- 
> 2.26.2
>