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.

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

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

On Tue, 11 Mar 2025 12:02:48 +0000 Lorenzo Stoakes <lorenzo.stoakes@oracle.com> wrote:

> 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!

Thank you for sharing the good finding!  I don't have a plan to address that
for now.

> 
> Anyway this seems sane, so:
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Thank you for your review!

> 
> 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.'

Thanks for this nice suggestion.  I will updte so in the next version.


Thanks,
SJ

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