linux-kernel - [PATCH 5/8] lib min_heap: add eqaware variant of min_heap_pop

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Message-Id: <20250610215516.1513296-6-visitorckw@gmail.com>
Date: Wed, 11 Jun 2025 05:55:13 +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 5/8] lib min_heap: add eqaware variant of min_heap_pop_push()

Introduce min_heap_pop_push_eqaware() as a variant of
min_heap_pop_push() 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 | 20 +++++++++++++++-----
 lib/min_heap.c           |  4 ++--
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
index 6c45d617b027..d7bf8dd0f6b1 100644
--- a/include/linux/min_heap.h
+++ b/include/linux/min_heap.h
@@ -424,15 +424,22 @@ bool __min_heap_pop_inline(min_heap_char *heap, size_t elem_size,
  */
 static __always_inline
 void __min_heap_pop_push_inline(min_heap_char *heap, const void *element, size_t elem_size,
-				const struct min_heap_callbacks *func, void *args)
+				const struct min_heap_callbacks *func, void *args, bool eqaware)
 {
+	siftdown_fn_t sift_down = eqaware ? __min_heap_sift_down_eqaware_inline :
+					    __min_heap_sift_down_inline;
+
 	memcpy(heap->data, element, elem_size);
-	__min_heap_sift_down_inline(heap, 0, elem_size, func, args);
+	sift_down(heap, 0, elem_size, func, args);
 }
 
 #define min_heap_pop_push_inline(_heap, _element, _func, _args)	\
 	__min_heap_pop_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
-				   __minheap_obj_size(_heap), _func, _args)
+				   __minheap_obj_size(_heap), _func, _args, false)
+
+#define min_heap_pop_push_eqaware_inline(_heap, _element, _func, _args)	\
+	__min_heap_pop_push_inline(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+				   __minheap_obj_size(_heap), _func, _args, true)
 
 /* Push an element on to the heap, O(log2(nr)). */
 static __always_inline
@@ -503,7 +510,7 @@ void __min_heapify_all(min_heap_char *heap, size_t elem_size,
 bool __min_heap_pop(min_heap_char *heap, size_t elem_size,
 		    const struct min_heap_callbacks *func, void *args, bool eqaware);
 void __min_heap_pop_push(min_heap_char *heap, const void *element, 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_push(min_heap_char *heap, const void *element, size_t elem_size,
 		     const struct min_heap_callbacks *func, void *args);
 bool __min_heap_del(min_heap_char *heap, size_t elem_size, size_t idx,
@@ -538,7 +545,10 @@ bool __min_heap_del(min_heap_char *heap, size_t elem_size, size_t idx,
 		       __minheap_obj_size(_heap), _func, _args, true)
 #define min_heap_pop_push(_heap, _element, _func, _args)	\
 	__min_heap_pop_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
-			    __minheap_obj_size(_heap), _func, _args)
+			    __minheap_obj_size(_heap), _func, _args, false)
+#define min_heap_pop_push_eqaware(_heap, _element, _func, _args)	\
+	__min_heap_pop_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
+			    __minheap_obj_size(_heap), _func, _args, true)
 #define min_heap_push(_heap, _element, _func, _args)	\
 	__min_heap_push(container_of(&(_heap)->nr, min_heap_char, nr), _element,	\
 			__minheap_obj_size(_heap), _func, _args)
diff --git a/lib/min_heap.c b/lib/min_heap.c
index dae3ed39421a..a69d8b80d443 100644
--- a/lib/min_heap.c
+++ b/lib/min_heap.c
@@ -56,9 +56,9 @@ bool __min_heap_pop(min_heap_char *heap, size_t elem_size,
 EXPORT_SYMBOL(__min_heap_pop);
 
 void __min_heap_pop_push(min_heap_char *heap, const void *element, size_t elem_size,
-			 const struct min_heap_callbacks *func, void *args)
+			 const struct min_heap_callbacks *func, void *args, bool eqaware)
 {
-	__min_heap_pop_push_inline(heap, element, elem_size, func, args);
+	__min_heap_pop_push_inline(heap, element, elem_size, func, args, eqaware);
 }
 EXPORT_SYMBOL(__min_heap_pop_push);
 
-- 
2.34.1