[PATCH v3 4/4] mm/page_owner: Record task command name

[Waiman Long <longman@redhat.com>]

The page_owner information currently includes the pid of the calling
task. That is useful as long as the task is still running. Otherwise,
the number is meaningless. To have more information about the allocating
tasks that had exited by the time the page_owner information is
retrieved, we need to store the command name of the task.

Add a new comm field into page_owner structure to store the command name
and display it when the page_owner information is retrieved. Only the
first 15 characters of the command name will be copied, but that should
be enough in most cases. Even for those commands with longer names,
it shouldn't be hard to guess what they are.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 mm/page_owner.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index a471c74c7fe0..8b2b381fd986 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -20,6 +20,7 @@
  * to use off stack temporal storage
  */
 #define PAGE_OWNER_STACK_DEPTH (16)
+#define PAGE_OWNER_COMM_LEN	16
 
 struct page_owner {
 	unsigned short order;
@@ -29,6 +30,7 @@ struct page_owner {
 	depot_stack_handle_t free_handle;
 	u64 ts_nsec;
 	u64 free_ts_nsec;
+	char comm[PAGE_OWNER_COMM_LEN];
 	pid_t pid;
 };
 
@@ -146,6 +148,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
 		page_owner = get_page_owner(page_ext);
 		page_owner->free_handle = handle;
 		page_owner->free_ts_nsec = free_ts_nsec;
+		page_owner->comm[0] = '\0';
 		page_ext = page_ext_next(page_ext);
 	}
 }
@@ -165,6 +168,8 @@ static inline void __set_page_owner_handle(struct page_ext *page_ext,
 		page_owner->last_migrate_reason = -1;
 		page_owner->pid = current->pid;
 		page_owner->ts_nsec = local_clock();
+		strlcpy(page_owner->comm, current->comm,
+			sizeof(page_owner->comm));
 		__set_bit(PAGE_EXT_OWNER, &page_ext->flags);
 		__set_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 
@@ -232,6 +237,7 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old)
 	new_page_owner->pid = old_page_owner->pid;
 	new_page_owner->ts_nsec = old_page_owner->ts_nsec;
 	new_page_owner->free_ts_nsec = old_page_owner->ts_nsec;
+	strcpy(new_page_owner->comm, old_page_owner->comm);
 
 	/*
 	 * We don't clear the bit on the old folio as it's going to be freed
@@ -376,10 +382,11 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 		return -ENOMEM;
 
 	ret = scnprintf(kbuf, count,
-			"Page allocated via order %u, mask %#x(%pGg), pid %d, ts %llu ns, free_ts %llu ns\n",
+			"Page allocated via order %u, mask %#x(%pGg), pid %d (%s), ts %llu ns, free_ts %llu ns\n",
 			page_owner->order, page_owner->gfp_mask,
 			&page_owner->gfp_mask, page_owner->pid,
-			page_owner->ts_nsec, page_owner->free_ts_nsec);
+			page_owner->comm, page_owner->ts_nsec,
+			page_owner->free_ts_nsec);
 
 	/* Print information relevant to grouping pages by mobility */
 	pageblock_mt = get_pageblock_migratetype(page);
@@ -446,9 +453,10 @@ void __dump_page_owner(const struct page *page)
 	else
 		pr_alert("page_owner tracks the page as freed\n");
 
-	pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg), pid %d, ts %llu, free_ts %llu\n",
+	pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg), pid %d (%s), ts %llu, free_ts %llu\n",
 		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask,
-		 page_owner->pid, page_owner->ts_nsec, page_owner->free_ts_nsec);
+		 page_owner->pid, page_owner->comm, page_owner->ts_nsec,
+		 page_owner->free_ts_nsec);
 
 	handle = READ_ONCE(page_owner->handle);
 	if (!handle)
-- 
2.27.0