[PATCH RFC 4/9] mm/page_owner: add 'xarray swap_page_owners' and helpers

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

Add 'xarray swap_page_owners' to index 'struct swap_page_owner' objects
by key 'swp_entry_t', and helpers to store, load, and erase.

This is used to track the allocation stack trace of pages in swap space.

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 mm/page_owner.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 19ccbda1c2a4..5cd7de1f8023 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -68,6 +68,7 @@ struct swap_page_owner {
 	pid_t pid;
 	pid_t tgid;
 };
+static DEFINE_XARRAY(swap_page_owners);
 #endif
 
 static depot_stack_handle_t dummy_handle;
@@ -461,6 +462,50 @@ static void free_swap_page_owner(void *spo)
 	kfree(spo);
 }
 
+static int store_swap_page_owner(struct swap_page_owner *spo, swp_entry_t entry)
+{
+	/* lookup the swap entry.val from the page */
+	void *ret = xa_store(&swap_page_owners, entry.val, spo, GFP_KERNEL);
+
+	if (WARN(xa_is_err(ret),
+	    "page_owner: swap: swp_entry not stored (%lu)\n", entry.val)) {
+		free_swap_page_owner(spo);
+		return xa_err(ret);
+	} else if (ret) {
+		/* Entry is being replaced, free the old entry */
+		free_swap_page_owner(ret);
+	}
+
+	return 0;
+}
+
+static void *load_swap_page_owner(swp_entry_t entry)
+{
+	void *spo = xa_load(&swap_page_owners, entry.val);
+
+	if (WARN(!spo,
+	    "page_owner: swap: swp_entry not loaded (%lu)\n", entry.val))
+		return NULL;
+
+	return spo;
+}
+
+static void erase_swap_page_owner(swp_entry_t entry, bool lock)
+{
+	void *spo;
+
+	if (lock)
+		spo = xa_erase(&swap_page_owners, entry.val);
+	else
+		spo = __xa_erase(&swap_page_owners, entry.val);
+
+	if (WARN(!spo,
+	    "page_owner: swap: swp_entry not erased (%lu)\n", entry.val))
+		return;
+
+	free_swap_page_owner(spo);
+}
+
 static void copy_to_swap_page_owner(struct swap_page_owner *spo,
 				    struct page_owner *page_owner)
 {
-- 
2.51.0