Re: [PATCH 3/9] mm/madvise: deduplicate madvise_do_behavior() skip case handlings

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Mar 10, 2025 at 10:23:12AM -0700, SeongJae Park wrote:
> The logic for checking if a given madvise() request for a single memory
> range can skip real work, namely madvise_do_behavior(), is duplicated in
> do_madvise() and vector_madvise().  Split out the logic to a function
> and resue it.

NIT: typo :)

>
> Signed-off-by: SeongJae Park <sj@kernel.org>

madvise_set_anon_name() seems to do something similar, but somewhat
differently... not sure if you address this in a later commit but worth
looking at too!

Anyway this seems sane, so:

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

Note nits!

> ---
>  mm/madvise.c | 53 +++++++++++++++++++++++++++++-----------------------
>  1 file changed, 30 insertions(+), 23 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 611db868ae38..764ec1f2475b 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1640,6 +1640,27 @@ static bool is_valid_madvise(unsigned long start, size_t len_in, int behavior)
>  	return true;
>  }
>
> +/*
> + * madvise_should_skip() - Return if an madivse request can skip real works.

NIT: 'real works' sounds strange.

I'd say something like 'if the specified behaviour is invalid or nothing
would occur, we skip this operation. In the former case we return an
error.'

> + * @start:	Start address of madvise-requested address range.
> + * @len_in:	Length of madvise-requested address range.
> + * @behavior:	Requested madvise behavor.
> + * @err:	Pointer to store an error code from the check.
> + */
> +static bool madvise_should_skip(unsigned long start, size_t len_in,
> +		int behavior, int *err)
> +{
> +	if (!is_valid_madvise(start, len_in, behavior)) {
> +		*err = -EINVAL;
> +		return true;
> +	}
> +	if (start + PAGE_ALIGN(len_in) == start) {
> +		*err = 0;
> +		return true;
> +	}
> +	return false;
> +}
> +
>  static bool is_madvise_populate(int behavior)
>  {
>  	switch (behavior) {
> @@ -1747,23 +1768,15 @@ static int madvise_do_behavior(struct mm_struct *mm,
>   */
>  int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior)
>  {
> -	unsigned long end;
>  	int error;
> -	size_t len;
> -
> -	if (!is_valid_madvise(start, len_in, behavior))
> -		return -EINVAL;
> -
> -	len = PAGE_ALIGN(len_in);
> -	end = start + len;
> -
> -	if (end == start)
> -		return 0;
>
> +	if (madvise_should_skip(start, len_in, behavior, &error))
> +		return error;
>  	error = madvise_lock(mm, behavior);
>  	if (error)
>  		return error;
> -	error = madvise_do_behavior(mm, start, len_in, len, behavior);
> +	error = madvise_do_behavior(mm, start, len_in, PAGE_ALIGN(len_in),
> +			behavior);
>  	madvise_unlock(mm, behavior);
>
>  	return error;
> @@ -1790,19 +1803,13 @@ static ssize_t vector_madvise(struct mm_struct *mm, struct iov_iter *iter,
>  	while (iov_iter_count(iter)) {
>  		unsigned long start = (unsigned long)iter_iov_addr(iter);
>  		size_t len_in = iter_iov_len(iter);
> -		size_t len;
> -
> -		if (!is_valid_madvise(start, len_in, behavior)) {
> -			ret = -EINVAL;
> -			break;
> -		}
> +		int error;
>
> -		len = PAGE_ALIGN(len_in);
> -		if (start + len == start)
> -			ret = 0;
> +		if (madvise_should_skip(start, len_in, behavior, &error))
> +			ret = error;
>  		else
> -			ret = madvise_do_behavior(mm, start, len_in, len,
> -					behavior);
> +			ret = madvise_do_behavior(mm, start, len_in,
> +					PAGE_ALIGN(len_in), behavior);
>  		/*
>  		 * An madvise operation is attempting to restart the syscall,
>  		 * but we cannot proceed as it would not be correct to repeat
> --
> 2.39.5