[PATCH RFC 3/9] mm/page_owner: add 'struct swap_page_owner' and helpers

[Mauricio Faria de Oliveira <mfo@igalia.com>]

Add 'struct swap_page_owner' to store the (initial) allocation stack trace
and some attributes, plus helpers to allocate, free, and copy it to/from
'struct page_owner'.

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 mm/page_owner.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index a27958872b07..19ccbda1c2a4 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -60,6 +60,14 @@ DEFINE_STATIC_KEY_FALSE(page_owner_inited);
 #ifdef CONFIG_SWAP_PAGE_OWNER
 static bool swap_page_owner_enabled __initdata;
 DEFINE_STATIC_KEY_FALSE(swap_page_owner_inited);
+
+struct swap_page_owner {
+	depot_stack_handle_t handle;
+	u64 ts_nsec;
+	char comm[TASK_COMM_LEN];
+	pid_t pid;
+	pid_t tgid;
+};
 #endif
 
 static depot_stack_handle_t dummy_handle;
@@ -442,6 +450,38 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old)
 	rcu_read_unlock();
 }
 
+#ifdef CONFIG_SWAP_PAGE_OWNER
+static void *alloc_swap_page_owner(void)
+{
+	return kmalloc(sizeof(struct swap_page_owner), GFP_KERNEL);
+}
+
+static void free_swap_page_owner(void *spo)
+{
+	kfree(spo);
+}
+
+static void copy_to_swap_page_owner(struct swap_page_owner *spo,
+				    struct page_owner *page_owner)
+{
+	spo->handle = page_owner->handle;
+	spo->ts_nsec = page_owner->ts_nsec;
+	spo->pid = page_owner->pid;
+	spo->tgid = page_owner->tgid;
+	strscpy(spo->comm, page_owner->comm, sizeof(page_owner->comm));
+}
+
+static void copy_from_swap_page_owner(struct page_owner *page_owner,
+				      struct swap_page_owner *spo)
+{
+	page_owner->handle = spo->handle;
+	page_owner->ts_nsec = spo->ts_nsec;
+	page_owner->pid = spo->pid;
+	page_owner->tgid = spo->tgid;
+	strscpy(page_owner->comm, spo->comm, sizeof(page_owner->comm));
+}
+#endif
+
 void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 				       pg_data_t *pgdat, struct zone *zone)
 {
-- 
2.51.0