linux-kernel - [PATCH 2/2] mm/numa_emulation: Move the size calculation in split_nodes

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Message-Id: <20250926-numa-emu-v1-2-714f2691bf8b@oss.qualcomm.com>
Date: Fri, 26 Sep 2025 16:04:50 +0530
From: pratyush.brahma@....qualcomm.com
To: Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Pratyush Brahma <pratyush.brahma@....qualcomm.com>
Subject: [PATCH 2/2] mm/numa_emulation: Move the size calculation in
 split_nodes_interleave() to a separate function

From: Pratyush Brahma <pratyush.brahma@....qualcomm.com>

The size calculation in split_nodes_interleave() has several nuances.
Move it to a separate function to improve code modularity and
simplify the readability of split_nodes_interleave().

Signed-off-by: Pratyush Brahma <pratyush.brahma@....qualcomm.com>
---
 mm/numa_emulation.c | 44 +++++++++++++++++++++++++++++---------------
 1 file changed, 29 insertions(+), 15 deletions(-)

diff --git a/mm/numa_emulation.c b/mm/numa_emulation.c
index 2a335b3dd46a..882c349c2a0f 100644
--- a/mm/numa_emulation.c
+++ b/mm/numa_emulation.c
@@ -76,6 +76,34 @@ static int __init emu_setup_memblk(struct numa_meminfo *ei,
 	return 0;
 }
 
+static void __init __calc_split_params(u64 addr, u64 max_addr,
+		int nr_nodes, u64 *psize, int *pbig)
+{
+	u64 size, usable_size;
+	int big;
+
+	/* total usable memory (skip holes) */
+	usable_size  = max_addr - addr - mem_hole_size(addr, max_addr);
+
+	/*
+	 * Calculate target node size.  x86_32 freaks on __udivdi3() so do
+	 * the division in ulong number of pages and convert back.
+	 */
+	size = PFN_PHYS((unsigned long)(usable_size >> PAGE_SHIFT) / nr_nodes);
+
+	/*
+	 * Calculate the number of big nodes that can be allocated as a result
+	 * of consolidating the remainder.
+	 */
+	big = ((size & (FAKE_NODE_MIN_SIZE - 1UL)) * nr_nodes) / FAKE_NODE_MIN_SIZE;
+
+	/* Align the base size down to the minimum granularity */
+	size = ALIGN_DOWN(size, FAKE_NODE_MIN_SIZE);
+
+	*psize = size;
+	*pbig  = big;
+}
+
 /*
  * Sets up nr_nodes fake nodes interleaved over physical nodes ranging from addr
  * to max_addr.
@@ -100,21 +128,7 @@ static int __init split_nodes_interleave(struct numa_meminfo *ei,
 		nr_nodes = MAX_NUMNODES;
 	}
 
-	/*
-	 * Calculate target node size.  x86_32 freaks on __udivdi3() so do
-	 * the division in ulong number of pages and convert back.
-	 */
-	size = max_addr - addr - mem_hole_size(addr, max_addr);
-	size = PFN_PHYS((unsigned long)(size >> PAGE_SHIFT) / nr_nodes);
-
-	/*
-	 * Calculate the number of big nodes that can be allocated as a result
-	 * of consolidating the remainder.
-	 */
-	big = ((size & (FAKE_NODE_MIN_SIZE - 1UL)) * nr_nodes) /
-		FAKE_NODE_MIN_SIZE;
-
-	size = ALIGN_DOWN(size, FAKE_NODE_MIN_SIZE);
+	__calc_split_params(addr, max_addr, nr_nodes, &size, &big);
 	if (!size) {
 		pr_err("Not enough memory for each node.  "
 			"NUMA emulation disabled.\n");

-- 
2.34.1