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

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Message-ID: <aF4etw9dELyW7FEZ@gourry-fedora-PF4VCD3F>
Date: Fri, 27 Jun 2025 00:31:51 -0400
From: Gregory Price <gourry@...rry.net>
To: Joshua Hahn <joshua.hahnjy@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Alistair Popple <apopple@...dia.com>,
	Byungchul Park <byungchul@...com>,
	David Hildenbrand <david@...hat.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Rakie Kim <rakie.kim@...com>,
	Ying Huang <ying.huang@...ux.alibaba.com>, Zi Yan <ziy@...dia.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-team@...a.com
Subject: Re: [PATCH 1/2] mm/mempolicy: Simplify weighted interleave bulk
 alloc calculations

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@...il.com>

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

Reviewed-by: Gregory Price <gourry@...rry.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