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

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Message-ID: <86cd01ca-2be8-4e20-83fb-1f9321da6349@redhat.com>
Date: Thu, 26 Jun 2025 23:51:32 +0200
From: David Hildenbrand <david@...hat.com>
To: Joshua Hahn <joshua.hahnjy@...il.com>, Gregory Price <gourry@...rry.net>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Alistair Popple <apopple@...dia.com>, Byungchul Park <byungchul@...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 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@...il.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@...hat.com>

-- 
Cheers,

David / dhildenb