linux-kernel - [PATCH 2/3] mm/percpu.c: optimize the code in pcpu_setup_first

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Date:   Fri, 21 Jul 2023 21:17:59 +0800
From:   Baoquan He <bhe@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, dennis@...nel.org,
        tj@...nel.org, cl@...ux.com, mawupeng1@...wei.com,
        Baoquan He <bhe@...hat.com>
Subject: [PATCH 2/3] mm/percpu.c: optimize the code in pcpu_setup_first_chunk() a little bit

This removes the need of local varibale 'chunk', and optimize the code
calling pcpu_alloc_first_chunk() to initialize reserved chunk and
dynamic chunk to make it simpler.

Signed-off-by: Baoquan He <bhe@...hat.com>
---
 mm/percpu.c | 32 +++++++++++++-------------------
 1 file changed, 13 insertions(+), 19 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 1480bf283d11..c25b058a46ad 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2581,7 +2581,6 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 {
 	size_t size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
 	size_t static_size, dyn_size;
-	struct pcpu_chunk *chunk;
 	unsigned long *group_offsets;
 	size_t *group_sizes;
 	unsigned long *unit_off;
@@ -2697,7 +2696,7 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 	pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
 	pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
 	pcpu_atom_size = ai->atom_size;
-	pcpu_chunk_struct_size = struct_size(chunk, populated,
+	pcpu_chunk_struct_size = struct_size((struct pcpu_chunk *)0, populated,
 					     BITS_TO_LONGS(pcpu_unit_pages));
 
 	pcpu_stats_save_ai(ai);
@@ -2735,28 +2734,23 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
 
 	/*
 	 * Initialize first chunk.
-	 * If the reserved_size is non-zero, this initializes the reserved
-	 * chunk.  If the reserved_size is zero, the reserved chunk is NULL
-	 * and the dynamic region is initialized here.  The first chunk,
-	 * pcpu_first_chunk, will always point to the chunk that serves
-	 * the dynamic region.
+	 * If the reserved_size is non-zero, initializes the reserved chunk
+	 * firstly. If the reserved_size is zero, the reserved chunk is NULL
+	 * and the dynamic region is initialized directly. The first chunk,
+	 * pcpu_first_chunk, will always point to the chunk that serves the
+	 * dynamic region.
 	 */
 	tmp_addr = (unsigned long)base_addr + static_size;
-	map_size = ai->reserved_size ?: dyn_size;
-	chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
-
-	/* init dynamic chunk if necessary */
 	if (ai->reserved_size) {
-		pcpu_reserved_chunk = chunk;
-
-		tmp_addr = (unsigned long)base_addr + static_size +
-			   ai->reserved_size;
-		map_size = dyn_size;
-		chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
+		map_size = ai->reserved_size;
+		pcpu_reserved_chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
 	}
 
-	/* link the first chunk in */
-	pcpu_first_chunk = chunk;
+	/* init dynamic chunk if necessary */
+	tmp_addr += (unsigned long)ai->reserved_size;
+	map_size = dyn_size;
+	pcpu_first_chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
+
 	pcpu_nr_empty_pop_pages = pcpu_first_chunk->nr_empty_pop_pages;
 	pcpu_chunk_relocate(pcpu_first_chunk, -1);
 
-- 
2.34.1