linux-kernel - [PATCH v2] percpu: simplify the logic of pcpu_alloc_first

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Date: Wed, 24 Apr 2024 16:27:30 +0800
From: Yuntao Wang <ytcoode@...il.com>
To: dennis@...nel.org
Cc: akpm@...ux-foundation.org,
	cl@...ux.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	tj@...nel.org,
	ytcoode@...il.com
Subject: [PATCH v2] percpu: simplify the logic of pcpu_alloc_first_chunk()

In the logic for hiding the end region of the chunk, there are several
places where the same value 'region_bits - offset_bits' is calculated
over and over again using different methods. Eliminating these redundant
calculations can improve code readability.

Additionally, there is a lot of repetitive code when hiding the start and
end regions of the chunk. We can consolidate this logic into a function,
making the final code cleaner and more concise.

Signed-off-by: Yuntao Wang <ytcoode@...il.com>
---
v1 -> v2: Optimize the code based on Dennis's suggestion

 mm/percpu.c | 27 ++++++++++++---------------
 1 file changed, 12 insertions(+), 15 deletions(-)

diff --git a/mm/percpu.c b/mm/percpu.c
index 4e11fc1e6def..d22b317f3d41 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1329,6 +1329,15 @@ static void pcpu_init_md_blocks(struct pcpu_chunk *chunk)
 		pcpu_init_md_block(md_block, PCPU_BITMAP_BLOCK_BITS);
 }
 
+static void pcpu_chunk_hide_region(struct pcpu_chunk *chunk, int bit_off,
+				   int bits)
+{
+	bitmap_set(chunk->alloc_map, bit_off, bits);
+	set_bit(bit_off, chunk->bound_map);
+	set_bit(bit_off + bits, chunk->bound_map);
+	pcpu_block_update_hint_alloc(chunk, bit_off, bits);
+}
+
 /**
  * pcpu_alloc_first_chunk - creates chunks that serve the first chunk
  * @tmp_addr: the start of the region served
@@ -1409,27 +1418,15 @@ static struct pcpu_chunk * __init pcpu_alloc_first_chunk(unsigned long tmp_addr,
 	if (chunk->start_offset) {
 		/* hide the beginning of the bitmap */
 		offset_bits = chunk->start_offset / PCPU_MIN_ALLOC_SIZE;
-		bitmap_set(chunk->alloc_map, 0, offset_bits);
-		set_bit(0, chunk->bound_map);
-		set_bit(offset_bits, chunk->bound_map);
-
 		chunk->chunk_md.first_free = offset_bits;
-
-		pcpu_block_update_hint_alloc(chunk, 0, offset_bits);
+		pcpu_chunk_hide_region(chunk, 0, offset_bits);
 	}
 
 	if (chunk->end_offset) {
 		/* hide the end of the bitmap */
 		offset_bits = chunk->end_offset / PCPU_MIN_ALLOC_SIZE;
-		bitmap_set(chunk->alloc_map,
-			   pcpu_chunk_map_bits(chunk) - offset_bits,
-			   offset_bits);
-		set_bit((start_offset + map_size) / PCPU_MIN_ALLOC_SIZE,
-			chunk->bound_map);
-		set_bit(region_bits, chunk->bound_map);
-
-		pcpu_block_update_hint_alloc(chunk, pcpu_chunk_map_bits(chunk)
-					     - offset_bits, offset_bits);
+		pcpu_chunk_hide_region(chunk, region_bits - offset_bits,
+				       offset_bits);
 	}
 
 	return chunk;
-- 
2.44.0