linux-kernel - Re: [PATCH] mm/THP: use hugepage_vma_check() in khugepaged_enter_vma

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Date:   Mon, 21 May 2018 15:53:02 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Song Liu <songliubraving@...com>, linux-mm@...ck.org
Cc:     kernel-team@...com, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH] mm/THP: use hugepage_vma_check() in
 khugepaged_enter_vma_merge()

On Mon, 2018-05-21 at 12:38 -0700, Song Liu wrote:

> This patch fixes these problems by reusing hugepage_vma_check() in
> khugepaged_enter_vma_merge().

Lets take a look at this in more detail. This effectively
adds the following conditions to khugepaged_enter_vma_merge:
- fail if MMF_DISABLE_THP bit is set in mm->flags (good)
- allow if merging a tmpfs file and THP tmpfs is enabled (good)
- disallow if is_vma_temporary_stack (good)
- otherwise, allow if !VM_NO_KHUGEPAGED flag (good)

Looks like this covers all the conditions I can think
of, and if I missed any, chances are that condition
should be added to hugepage_vma_check()...

> Signed-off-by: Song Liu <songliubraving@...com>

Reviewed-by: Rik van Riel <riel@...riel.com>

> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index d7b2a4b..e50c2bd 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -430,18 +430,14 @@ int __khugepaged_enter(struct mm_struct *mm)
>  	return 0;
>  }
>  
> +static bool hugepage_vma_check(struct vm_area_struct *vma);
> +
>  int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
>  			       unsigned long vm_flags)
>  {
>  	unsigned long hstart, hend;
> -	if (!vma->anon_vma)
> -		/*
> -		 * Not yet faulted in so we will register later in
> the
> -		 * page fault if needed.
> -		 */
> -		return 0;
> -	if (vma->vm_ops || (vm_flags & VM_NO_KHUGEPAGED))
> -		/* khugepaged not yet working on file or special
> mappings */
> +
> +	if (!hugepage_vma_check(vma))
>  		return 0;
>  	hstart = (vma->vm_start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
>  	hend = vma->vm_end & HPAGE_PMD_MASK;
-- 
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