linux-kernel - [PATCH] mm: cma: Set early_pfn and bitmap as a union in cma

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Message-Id: <20250509083528.1360952-1-hezhongkun.hzk@bytedance.com>
Date: Fri,  9 May 2025 16:35:28 +0800
From: Zhongkun He <hezhongkun.hzk@...edance.com>
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Zhongkun He <hezhongkun.hzk@...edance.com>
Subject: [PATCH] mm: cma: Set early_pfn and bitmap as a union in cma_memrange

Since early_pfn and bitmap are never used at the same time,
they can be defined as a union to reduce the size of the
data structure. This change can save 8 * u64 entries per CMA.

Signed-off-by: Zhongkun He <hezhongkun.hzk@...edance.com>
---
 mm/cma.c | 11 ++++++-----
 mm/cma.h |  6 ++++--
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 15632939f20a..ec4b9a401b7d 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -143,13 +143,14 @@ bool cma_validate_zones(struct cma *cma)
 
 static void __init cma_activate_area(struct cma *cma)
 {
-	unsigned long pfn, end_pfn;
+	unsigned long pfn, end_pfn, early_pfn[CMA_MAX_RANGES];
 	int allocrange, r;
 	struct cma_memrange *cmr;
 	unsigned long bitmap_count, count;
 
 	for (allocrange = 0; allocrange < cma->nranges; allocrange++) {
 		cmr = &cma->ranges[allocrange];
+		early_pfn[allocrange] = cmr->early_pfn;
 		cmr->bitmap = bitmap_zalloc(cma_bitmap_maxno(cma, cmr),
 					    GFP_KERNEL);
 		if (!cmr->bitmap)
@@ -161,13 +162,13 @@ static void __init cma_activate_area(struct cma *cma)
 
 	for (r = 0; r < cma->nranges; r++) {
 		cmr = &cma->ranges[r];
-		if (cmr->early_pfn != cmr->base_pfn) {
-			count = cmr->early_pfn - cmr->base_pfn;
+		if (early_pfn[r] != cmr->base_pfn) {
+			count = early_pfn[r] - cmr->base_pfn;
 			bitmap_count = cma_bitmap_pages_to_bits(cma, count);
 			bitmap_set(cmr->bitmap, 0, bitmap_count);
 		}
 
-		for (pfn = cmr->early_pfn; pfn < cmr->base_pfn + cmr->count;
+		for (pfn = early_pfn[r]; pfn < cmr->base_pfn + cmr->count;
 		     pfn += pageblock_nr_pages)
 			init_cma_reserved_pageblock(pfn_to_page(pfn));
 	}
@@ -193,7 +194,7 @@ static void __init cma_activate_area(struct cma *cma)
 		for (r = 0; r < allocrange; r++) {
 			cmr = &cma->ranges[r];
 			end_pfn = cmr->base_pfn + cmr->count;
-			for (pfn = cmr->early_pfn; pfn < end_pfn; pfn++)
+			for (pfn = early_pfn[r]; pfn < end_pfn; pfn++)
 				free_reserved_page(pfn_to_page(pfn));
 		}
 	}
diff --git a/mm/cma.h b/mm/cma.h
index 41a3ab0ec3de..c70180c36559 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -25,9 +25,11 @@ struct cma_kobject {
  */
 struct cma_memrange {
 	unsigned long base_pfn;
-	unsigned long early_pfn;
 	unsigned long count;
-	unsigned long *bitmap;
+	union {
+		unsigned long early_pfn;
+		unsigned long *bitmap;
+	};
 #ifdef CONFIG_CMA_DEBUGFS
 	struct debugfs_u32_array dfs_bitmap;
 #endif
-- 
2.39.5