[PATCH v2] mm: oom_kill: add trace logs in process_mrelease() system call

[Pratyush Brahma]

From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>

The process_mrelease() system call[1] is used to release the memory of
a dying process from the context of the caller, which is similar to and
uses the functions of the oom reaper logic. There exists trace logs for
a process when reaped by the oom reaper. Just extend the same to when
done by the process_mrelease() system call.

[1]
https://lore.kernel.org/linux-mm/20210809185259.405936-1-surenb@xxxxxxxxxx/

Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx>
Signed-off-by: Pratyush Brahma <quic_pbrahma@xxxxxxxxxxx>
---
Changes in v2:
- Added trace_skip_task_reaping() to cover more cases where we skip
  reaping.
- Print debug information in pr_debug instead of pr_info
- The original author email domain has changed. Update the new email
  address.

[v1]
https://patchwork.kernel.org/project/linux-mm/patch/1629106756-20874-1-git-send-email-charante@xxxxxxxxxxxxxx/

 mm/oom_kill.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 3c6cf9e3cd66..51ad5f0b612e 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -995,7 +995,6 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
 	mmdrop(mm);
 	put_task_struct(victim);
 }
-#undef K
 
 /*
  * Kill provided task unless it's secured by setting
@@ -1241,17 +1240,33 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
 		goto drop_mm;
 
 	if (mmap_read_lock_killable(mm)) {
+		trace_skip_task_reaping(task->pid);
 		ret = -EINTR;
-		goto drop_mm;
+		goto read_unlock;
 	}
 	/*
 	 * Check MMF_OOM_SKIP again under mmap_read_lock protection to ensure
 	 * possible change in exit_mmap is seen
 	 */
-	if (!test_bit(MMF_OOM_SKIP, &mm->flags) && !__oom_reap_task_mm(mm))
+	if (test_bit(MMF_OOM_SKIP, &mm->flags)) {
+		trace_skip_task_reaping(task->pid);
+		goto read_unlock;
+	}
+
+	trace_start_task_reaping(task->pid);
+
+	if (!__oom_reap_task_mm(mm))
 		ret = -EAGAIN;
-	mmap_read_unlock(mm);
 
+	pr_debug("process_mrelease: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
+						task_pid_nr(task), task->comm,
+						K(get_mm_counter(mm, MM_ANONPAGES)),
+						K(get_mm_counter(mm, MM_FILEPAGES)),
+						K(get_mm_counter(mm, MM_SHMEMPAGES)));
+	trace_finish_task_reaping(task->pid);
+
+read_unlock:
+	mmap_read_unlock(mm);
 drop_mm:
 	mmdrop(mm);
 put_task:
@@ -1261,3 +1276,4 @@ SYSCALL_DEFINE2(process_mrelease, int, pidfd, unsigned int, flags)
 	return -ENOSYS;
 #endif /* CONFIG_MMU */
 }
+#undef K
-- 
2.17.1