linux-kernel - [PATCH v2 1/5] mm/page_owner: introduce struct stack_print

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Message-ID: <20251001175611.575861-2-mfo@igalia.com>
Date: Wed,  1 Oct 2025 14:56:07 -0300
From: Mauricio Faria de Oliveira <mfo@...lia.com>
To: Michal Hocko <mhocko@...e.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: Oscar Salvador <osalvador@...e.de>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Brendan Jackman <jackmanb@...gle.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Zi Yan <ziy@...dia.com>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel-dev@...lia.com
Subject: [PATCH v2 1/5] mm/page_owner: introduce struct stack_print_ctx

Currently, struct seq_file.private is used as an iterator in stack_list
by stack_start|next(), for stack_print().

Create a context struct for this, in order to add another field next.

No behavior change intended.

P.S.: page_owner_stack_open() is expanded with separate statements for
variable definition and return just in preparation for the next patch.

Signed-off-by: Mauricio Faria de Oliveira <mfo@...lia.com>
---
 mm/page_owner.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index c3ca21132c2c..c1a7d7afe945 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -45,6 +45,10 @@ static struct stack failure_stack;
 static struct stack *stack_list;
 static DEFINE_SPINLOCK(stack_list_lock);
 
+struct stack_print_ctx {
+	struct stack *stack;
+};
+
 static bool page_owner_enabled __initdata;
 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
 
@@ -856,6 +860,7 @@ static const struct file_operations proc_page_owner_operations = {
 static void *stack_start(struct seq_file *m, loff_t *ppos)
 {
 	struct stack *stack;
+	struct stack_print_ctx *ctx = m->private;
 
 	if (*ppos == -1UL)
 		return NULL;
@@ -867,9 +872,9 @@ static void *stack_start(struct seq_file *m, loff_t *ppos)
 		 * value of stack_list.
 		 */
 		stack = smp_load_acquire(&stack_list);
-		m->private = stack;
+		ctx->stack = stack;
 	} else {
-		stack = m->private;
+		stack = ctx->stack;
 	}
 
 	return stack;
@@ -878,10 +883,11 @@ static void *stack_start(struct seq_file *m, loff_t *ppos)
 static void *stack_next(struct seq_file *m, void *v, loff_t *ppos)
 {
 	struct stack *stack = v;
+	struct stack_print_ctx *ctx = m->private;
 
 	stack = stack->next;
 	*ppos = stack ? *ppos + 1 : -1UL;
-	m->private = stack;
+	ctx->stack = stack;
 
 	return stack;
 }
@@ -926,7 +932,10 @@ static const struct seq_operations page_owner_stack_op = {
 
 static int page_owner_stack_open(struct inode *inode, struct file *file)
 {
-	return seq_open_private(file, &page_owner_stack_op, 0);
+	int ret = seq_open_private(file, &page_owner_stack_op,
+				   sizeof(struct stack_print_ctx));
+
+	return ret;
 }
 
 static const struct file_operations page_owner_stack_operations = {
-- 
2.48.1