linux-kernel - Re: [RFC PATCH 02/16] mm/madvise: split out populate behavior check logic

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Message-ID: <kic3iznofvqvkljvelk6c7l2jigdwtlrrlhebkrh4tnundfp6h@upfyjh5hr6k5>
Date: Wed, 5 Mar 2025 12:32:52 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: SeongJae Park <sj@...nel.org>
Cc: "Liam R. Howlett" <howlett@...il.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, kernel-team@...a.com, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [RFC PATCH 02/16] mm/madvise: split out populate behavior check
 logic

On Wed, Mar 05, 2025 at 10:15:57AM -0800, SeongJae Park wrote:
> madvise_do_behavior() has a long open-coded 'behavior' check for
> MADV_POPULATE_{READ,WRITE}.  It adds multiple layers[1] and make the
> code arguably take longer time to read.  Like is_memory_failure(), split
> out the check to a separate function.  This is not technically removing
> the additional layer but discourage further extending the switch-case.
> Also it makes madvise_do_behavior() code shorter and therefore easier to
> read.
> 
> [1] https://lore.kernel.org/bd6d0bf1-c79e-46bd-a810-9791efb9ad73@lucifer.local
> 
> Signed-off-by: SeongJae Park <sj@...nel.org>
> ---
>  mm/madvise.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/madvise.c b/mm/madvise.c
> index dbc8fec05cc6..4a91590656dc 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1633,6 +1633,17 @@ static bool is_valid_madvise(unsigned long start, size_t len_in, int behavior)
>  	return true;
>  }
>  
> +static bool is_memory_populate(int behavior)

No strong opinion on this patch but if you want to keep it, the above
name feels weird. How about either is_madvise_populate() or
is_populate_memory()?

> +{
> +	switch (behavior) {
> +	case MADV_POPULATE_READ:
> +	case MADV_POPULATE_WRITE:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
>  static int madvise_do_behavior(struct mm_struct *mm,
>  		unsigned long start, size_t len_in, size_t len, int behavior)
>  {
> @@ -1646,16 +1657,11 @@ static int madvise_do_behavior(struct mm_struct *mm,
>  	end = start + len;
>  
>  	blk_start_plug(&plug);
> -	switch (behavior) {
> -	case MADV_POPULATE_READ:
> -	case MADV_POPULATE_WRITE:
> +	if (is_memory_populate(behavior))
>  		error = madvise_populate(mm, start, end, behavior);
> -		break;
> -	default:
> +	else
>  		error = madvise_walk_vmas(mm, start, end, behavior,
>  					  madvise_vma_behavior);
> -		break;
> -	}
>  	blk_finish_plug(&plug);
>  	return error;
>  }
> -- 
> 2.39.5