mm/mempolicy: Cleanup and optimization for weighted interleave

[PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk alloc calculations

Posted by Joshua Hahn 3 months, 1 week ago

Simplify the math used to figure out how many pages should be allocated
per node. Instead of making conditional additions and deletions, we can just
make them unconditional by using min(). No functional changes intended.

Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>

---
 mm/mempolicy.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 3b1dfd08338b..78ad74a0e249 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2645,18 +2645,15 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
 	for (i = 0; i < nnodes; i++) {
 		node = next_node_in(prev_node, nodes);
 		weight = weights[node];
-		node_pages = weight * rounds;
-		/* If a delta exists, add this node's portion of the delta */
-		if (delta > weight) {
-			node_pages += weight;
-			delta -= weight;
-		} else if (delta) {
-			/* when delta is depleted, resume from that node */
-			node_pages += delta;
+		/* when delta is depleted, resume from that node */
+		if (delta && delta < weight) {
 			resume_node = node;
 			resume_weight = weight - delta;
-			delta = 0;
 		}
+		/* Add the node's portion of the delta, if there is one */
+		node_pages = weight * rounds + min(delta, weight);
+		delta -= min(delta, weight);
+
 		/* node_pages can be 0 if an allocation fails and rounds == 0 */
 		if (!node_pages)
 			break;
-- 
2.47.1

Re: [PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk alloc calculations

Posted by Oscar Salvador 3 months, 1 week ago

On Thu, Jun 26, 2025 at 01:09:33PM -0700, Joshua Hahn wrote:
> Simplify the math used to figure out how many pages should be allocated
> per node. Instead of making conditional additions and deletions, we can just
> make them unconditional by using min(). No functional changes intended.
> 
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>

Reviewed-by: Oscar Salvador <osalvador@suse.de>


-- 
Oscar Salvador
SUSE Labs

Re: [PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk alloc calculations

Posted by Rakie Kim 3 months, 1 week ago

On Thu, 26 Jun 2025 13:09:33 -0700 Joshua Hahn <joshua.hahnjy@gmail.com> wrote:
> Simplify the math used to figure out how many pages should be allocated
> per node. Instead of making conditional additions and deletions, we can just
> make them unconditional by using min(). No functional changes intended.
> 
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> 
> ---
>  mm/mempolicy.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3b1dfd08338b..78ad74a0e249 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2645,18 +2645,15 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
>  	for (i = 0; i < nnodes; i++) {
>  		node = next_node_in(prev_node, nodes);
>  		weight = weights[node];
> -		node_pages = weight * rounds;
> -		/* If a delta exists, add this node's portion of the delta */
> -		if (delta > weight) {
> -			node_pages += weight;
> -			delta -= weight;
> -		} else if (delta) {
> -			/* when delta is depleted, resume from that node */
> -			node_pages += delta;
> +		/* when delta is depleted, resume from that node */
> +		if (delta && delta < weight) {
>  			resume_node = node;
>  			resume_weight = weight - delta;
> -			delta = 0;
>  		}
> +		/* Add the node's portion of the delta, if there is one */
> +		node_pages = weight * rounds + min(delta, weight);
> +		delta -= min(delta, weight);
> +
>  		/* node_pages can be 0 if an allocation fails and rounds == 0 */
>  		if (!node_pages)
>  			break;
> -- 
> 2.47.1
> 

The updated logic improves clarity and readability. Well structured change.

Reviewed-by: Rakie Kim <rakie.kim@sk.com>

Re: [PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk alloc calculations

Posted by Gregory Price 3 months, 1 week ago

On Thu, Jun 26, 2025 at 01:09:33PM -0700, Joshua Hahn wrote:
> Simplify the math used to figure out how many pages should be allocated
> per node. Instead of making conditional additions and deletions, we can just
> make them unconditional by using min(). No functional changes intended.
> 
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>

you're better at concise math than I am :]

Reviewed-by: Gregory Price <gourry@gourry.net>

> 
> ---
>  mm/mempolicy.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3b1dfd08338b..78ad74a0e249 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2645,18 +2645,15 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
>  	for (i = 0; i < nnodes; i++) {
>  		node = next_node_in(prev_node, nodes);
>  		weight = weights[node];
> -		node_pages = weight * rounds;
> -		/* If a delta exists, add this node's portion of the delta */
> -		if (delta > weight) {
> -			node_pages += weight;
> -			delta -= weight;
> -		} else if (delta) {
> -			/* when delta is depleted, resume from that node */
> -			node_pages += delta;
> +		/* when delta is depleted, resume from that node */
> +		if (delta && delta < weight) {
>  			resume_node = node;
>  			resume_weight = weight - delta;
> -			delta = 0;
>  		}
> +		/* Add the node's portion of the delta, if there is one */
> +		node_pages = weight * rounds + min(delta, weight);
> +		delta -= min(delta, weight);
> +
>  		/* node_pages can be 0 if an allocation fails and rounds == 0 */
>  		if (!node_pages)
>  			break;
> -- 
> 2.47.1

Re: [PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk alloc calculations

Posted by David Hildenbrand 3 months, 1 week ago

On 26.06.25 22:09, Joshua Hahn wrote:
> Simplify the math used to figure out how many pages should be allocated
> per node. Instead of making conditional additions and deletions, we can just
> make them unconditional by using min(). No functional changes intended.
> 
> Signed-off-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> 
> ---
>   mm/mempolicy.c | 15 ++++++---------
>   1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 3b1dfd08338b..78ad74a0e249 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2645,18 +2645,15 @@ static unsigned long alloc_pages_bulk_weighted_interleave(gfp_t gfp,
>   	for (i = 0; i < nnodes; i++) {
>   		node = next_node_in(prev_node, nodes);
>   		weight = weights[node];
> -		node_pages = weight * rounds;
> -		/* If a delta exists, add this node's portion of the delta */
> -		if (delta > weight) {
> -			node_pages += weight;
> -			delta -= weight;
> -		} else if (delta) {
> -			/* when delta is depleted, resume from that node */
> -			node_pages += delta;
> +		/* when delta is depleted, resume from that node */
> +		if (delta && delta < weight) {
>   			resume_node = node;
>   			resume_weight = weight - delta;
> -			delta = 0;
>   		}
> +		/* Add the node's portion of the delta, if there is one */
> +		node_pages = weight * rounds + min(delta, weight);
> +		delta -= min(delta, weight);
> +

LGTM, but took me a second (and it's a bit late ...)

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb