linux-kernel - Re: [PATCH 2/9] mm/madvise: split out populate behavior check logic

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Message-ID: <e327026f-22bd-45fd-b3e5-fbf7246c3ec4@lucifer.local>
Date: Tue, 11 Mar 2025 11:29:19 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: SeongJae Park <sj@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R. Howlett" <howlett@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>,
        Vlastimil Babka <vbabka@...e.cz>, kernel-team@...a.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/9] mm/madvise: split out populate behavior check logic

On Mon, Mar 10, 2025 at 10:23:11AM -0700, 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>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  mm/madvise.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index c3ab1f283b18..611db868ae38 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1640,6 +1640,17 @@ static bool is_valid_madvise(unsigned long start, size_t len_in, int behavior)
>  	return true;
>  }
>
> +static bool is_madvise_populate(int behavior)
> +{
> +	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)
>  {
> @@ -1653,16 +1664,11 @@ 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_madvise_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