linux-kernel - [PATCH 3/8] lib min_heap: add eqaware variant of min_heapify

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Message-Id: <20250610215516.1513296-4-visitorckw@gmail.com>
Date: Wed, 11 Jun 2025 05:55:11 +0800
From: Kuan-Wei Chiu <visitorckw@...il.com>
To: corbet@....net,
	colyli@...nel.org,
	kent.overstreet@...ux.dev,
	akpm@...ux-foundation.org,
	robertpang@...gle.com
Cc: linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-bcache@...r.kernel.org,
	jserv@...s.ncku.edu.tw,
	Kuan-Wei Chiu <visitorckw@...il.com>,
	stable@...r.kernel.org
Subject: [PATCH 3/8] lib min_heap: add eqaware variant of min_heapify_all()

Introduce min_heapify_all_eqaware() as a variant of min_heapify_all()
that uses the equality-aware version of sift_down, which is implemented
in a top-down manner.

This top-down sift_down reduces the number of comparisons from
O(log2(n)) to O(1) in cases where many elements have equal priority. It
enables more efficient heap construction when the heap contains a large
number of equal elements.

Cc: stable@...r.kernel.org # 6.11+
Signed-off-by: Kuan-Wei Chiu <visitorckw@...il.com>
---
 include/linux/min_heap.h | 19 ++++++++++++++-----
 lib/min_heap.c           |  4 ++--
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
index 4cd8fd9db259..c2f6e1450505 100644
--- a/include/linux/min_heap.h
+++ b/include/linux/min_heap.h
@@ -371,17 +371,23 @@ void __min_heap_sift_up_inline(min_heap_char *heap, size_t elem_size, size_t idx
 /* Floyd's approach to heapification that is O(nr). */
 static __always_inline
 void __min_heapify_all_inline(min_heap_char *heap, size_t elem_size,
-			      const struct min_heap_callbacks *func, void *args)
+			      const struct min_heap_callbacks *func, void *args, bool eqaware)
 {
 	ssize_t i;
+	siftdown_fn_t sift_down = eqaware ? __min_heap_sift_down_eqaware_inline :
+					    __min_heap_sift_down_inline;
 
 	for (i = heap->nr / 2 - 1; i >= 0; i--)
-		__min_heap_sift_down_inline(heap, i, elem_size, func, args);
+		sift_down(heap, i, elem_size, func, args);
 }
 
 #define min_heapify_all_inline(_heap, _func, _args)	\
 	__min_heapify_all_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
-				 __minheap_obj_size(_heap), _func, _args)
+				 __minheap_obj_size(_heap), _func, _args, false)
+
+#define min_heapify_all_eqaware_inline(_heap, _func, _args)	\
+	__min_heapify_all_inline(container_of(&(_heap)->nr, min_heap_char, nr),	\
+				 __minheap_obj_size(_heap), _func, _args, true)
 
 /* Remove minimum element from the heap, O(log2(nr)). */
 static __always_inline
@@ -487,7 +493,7 @@ void __min_heap_sift_down_eqaware(min_heap_char *heap, size_t pos, size_t elem_s
 void __min_heap_sift_up(min_heap_char *heap, size_t elem_size, size_t idx,
 			const struct min_heap_callbacks *func, void *args);
 void __min_heapify_all(min_heap_char *heap, size_t elem_size,
-		       const struct min_heap_callbacks *func, void *args);
+		       const struct min_heap_callbacks *func, void *args, bool eqaware);
 bool __min_heap_pop(min_heap_char *heap, size_t elem_size,
 		    const struct min_heap_callbacks *func, void *args);
 void __min_heap_pop_push(min_heap_char *heap, const void *element, size_t elem_size,
@@ -514,7 +520,10 @@ bool __min_heap_del(min_heap_char *heap, size_t elem_size, size_t idx,
 			   __minheap_obj_size(_heap), _idx, _func, _args)
 #define min_heapify_all(_heap, _func, _args)	\
 	__min_heapify_all(container_of(&(_heap)->nr, min_heap_char, nr),	\
-			  __minheap_obj_size(_heap), _func, _args)
+			  __minheap_obj_size(_heap), _func, _args, false)
+#define min_heapify_all_eqaware(_heap, _func, _args)	\
+	__min_heapify_all(container_of(&(_heap)->nr, min_heap_char, nr),	\
+			  __minheap_obj_size(_heap), _func, _args, true)
 #define min_heap_pop(_heap, _func, _args)	\
 	__min_heap_pop(container_of(&(_heap)->nr, min_heap_char, nr),	\
 		       __minheap_obj_size(_heap), _func, _args)
diff --git a/lib/min_heap.c b/lib/min_heap.c
index 2225f40d0d7a..a422cfaff196 100644
--- a/lib/min_heap.c
+++ b/lib/min_heap.c
@@ -42,9 +42,9 @@ void __min_heap_sift_up(min_heap_char *heap, size_t elem_size, size_t idx,
 EXPORT_SYMBOL(__min_heap_sift_up);
 
 void __min_heapify_all(min_heap_char *heap, size_t elem_size,
-		       const struct min_heap_callbacks *func, void *args)
+		       const struct min_heap_callbacks *func, void *args, bool eqaware)
 {
-	__min_heapify_all_inline(heap, elem_size, func, args);
+	__min_heapify_all_inline(heap, elem_size, func, args, eqaware);
 }
 EXPORT_SYMBOL(__min_heapify_all);
 
-- 
2.34.1