From 0d9521b9b526a264a46c42fcde5d3d9a7cb490ea Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Fri, 24 Sep 2021 21:59:46 +0100
Subject: [PATCH] io-wq: add io_wq_work_node based stack
Git-commit: 0d9521b9b526a264a46c42fcde5d3d9a7cb490ea
Patch-mainline: v5.16-rc1
References: bsc#1205205

Apart from just using lists (i.e. io_wq_work_list), we also want to have
stacks, which are a bit faster, and have some interoperability between
them. Add a stack implementation based on io_wq_work_node and some
helpers.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/5d3a412a5ac0d47e0f0499d70d2207d70a68925e.1632516769.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
 fs/io-wq.h | 57 +++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 50 insertions(+), 7 deletions(-)

diff --git a/fs/io-wq.h b/fs/io-wq.h
index bf5c4c533760..c870062105d1 100644
--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -29,6 +29,15 @@ struct io_wq_work_list {
 	struct io_wq_work_node *last;
 };
 
+#define wq_list_for_each(pos, prv, head)			\
+	for (pos = (head)->first, prv = NULL; pos; prv = pos, pos = (pos)->next)
+
+#define wq_list_empty(list)	(READ_ONCE((list)->first) == NULL)
+#define INIT_WQ_LIST(list)	do {				\
+	(list)->first = NULL;					\
+	(list)->last = NULL;					\
+} while (0)
+
 static inline void wq_list_add_after(struct io_wq_work_node *node,
 				     struct io_wq_work_node *pos,
 				     struct io_wq_work_list *list)
@@ -54,6 +63,15 @@ static inline void wq_list_add_tail(struct io_wq_work_node *node,
 	}
 }
 
+static inline void wq_list_add_head(struct io_wq_work_node *node,
+				    struct io_wq_work_list *list)
+{
+	node->next = list->first;
+	if (!node->next)
+		list->last = node;
+	WRITE_ONCE(list->first, node);
+}
+
 static inline void wq_list_cut(struct io_wq_work_list *list,
 			       struct io_wq_work_node *last,
 			       struct io_wq_work_node *prev)
@@ -69,6 +87,31 @@ static inline void wq_list_cut(struct io_wq_work_list *list,
 	last->next = NULL;
 }
 
+static inline void __wq_list_splice(struct io_wq_work_list *list,
+				    struct io_wq_work_node *to)
+{
+	list->last->next = to->next;
+	to->next = list->first;
+	INIT_WQ_LIST(list);
+}
+
+static inline bool wq_list_splice(struct io_wq_work_list *list,
+				  struct io_wq_work_node *to)
+{
+	if (!wq_list_empty(list)) {
+		__wq_list_splice(list, to);
+		return true;
+	}
+	return false;
+}
+
+static inline void wq_stack_add_head(struct io_wq_work_node *node,
+				     struct io_wq_work_node *stack)
+{
+	node->next = stack->next;
+	stack->next = node;
+}
+
 static inline void wq_list_del(struct io_wq_work_list *list,
 			       struct io_wq_work_node *node,
 			       struct io_wq_work_node *prev)
@@ -76,14 +119,14 @@ static inline void wq_list_del(struct io_wq_work_list *list,
 	wq_list_cut(list, node, prev);
 }
 
-#define wq_list_for_each(pos, prv, head)			\
-	for (pos = (head)->first, prv = NULL; pos; prv = pos, pos = (pos)->next)
+static inline
+struct io_wq_work_node *wq_stack_extract(struct io_wq_work_node *stack)
+{
+	struct io_wq_work_node *node = stack->next;
 
-#define wq_list_empty(list)	(READ_ONCE((list)->first) == NULL)
-#define INIT_WQ_LIST(list)	do {				\
-	(list)->first = NULL;					\
-	(list)->last = NULL;					\
-} while (0)
+	stack->next = node->next;
+	return node;
+}
 
 struct io_wq_work {
 	struct io_wq_work_node list;
-- 
2.35.3