mm/page_owner.c: record tgid

In a single-threaded process, the pid in kernel task_struct is the same
as the tgid, which can mark the process of page allocation.  But in a
multithreaded process, only the task_struct of the thread leader has the
same pid as tgid, and the pids of other threads are different from tgid.
Therefore, tgid is recorded to provide effective information for
debugging and data statistics of multithreaded programs.

This can also be achieved by observing the task name (executable file
name) for a specific process.  However, when the same program is started
multiple times, the task name is the same and the tgid is different.
Therefore, in the debugging of multi-threaded programs, combined with
the task name and tgid, more accurate runtime information of a certain
run of the program can be obtained.

Link: https://lkml.kernel.org/r/20220219180450.2399-1-caoyixuan2019@email.szu.edu.cnSigned-off-by: Yixuan Cao <caoyixuan2019@email.szu.edu.cn>
Cc: Waiman Long <longman@redhat.com>
Cc: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_owner.c

@@ -31,6 +31,7 @@ struct page_owner {
 	u64 free_ts_nsec;
 	char comm[TASK_COMM_LEN];
 	pid_t pid;
+	pid_t tgid;
 };
 
 static bool page_owner_enabled = false;
@@ -165,6 +166,7 @@ static inline void __set_page_owner_handle(struct page_ext *page_ext,
 		page_owner->gfp_mask = gfp_mask;
 		page_owner->last_migrate_reason = -1;
 		page_owner->pid = current->pid;
+		page_owner->tgid = current->tgid;
 		page_owner->ts_nsec = local_clock();
 		strlcpy(page_owner->comm, current->comm,
 			sizeof(page_owner->comm));
@@ -233,6 +235,7 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old)
 		old_page_owner->last_migrate_reason;
 	new_page_owner->handle = old_page_owner->handle;
 	new_page_owner->pid = old_page_owner->pid;
+	new_page_owner->tgid = old_page_owner->tgid;
 	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);
@@ -383,11 +386,11 @@ 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 (%s), ts %llu ns, free_ts %llu ns\n",
+			"Page allocated via order %u, mask %#x(%pGg), pid %d, tgid %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->comm, page_owner->ts_nsec,
-			page_owner->free_ts_nsec);
+			page_owner->tgid, 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);
@@ -454,10 +457,10 @@ 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 (%s), ts %llu, free_ts %llu\n",
+	pr_alert("page last allocated via order %u, migratetype %s, gfp_mask %#x(%pGg), pid %d, tgid %d (%s), ts %llu, free_ts %llu\n",
 		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask,
-		 page_owner->pid, page_owner->comm, page_owner->ts_nsec,
-		 page_owner->free_ts_nsec);
+		 page_owner->pid, page_owner->tgid, page_owner->comm,
+		 page_owner->ts_nsec, page_owner->free_ts_nsec);
 
 	handle = READ_ONCE(page_owner->handle);
 	if (!handle)