[PATCH v2] mm: add warning if __vm_enough_memory fails

[Kefeng Wang]

If a process has no enough memory to allocate a new virtual mapping, we
may meet kinds of error, eg, fork cannot allocate memory, SIGBUS error
in shmem, but it is difficult to confirm them, let's add some debug
information to easy to check this scenario if __vm_enough_memory fails.

Reported-by: Yongqiang Liu <liuyongqiang13@xxxxxxxxxx>
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
v2: use pr_warn_ratelimited, suggested by David Hildenbrand

 mm/util.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/util.c b/mm/util.c
index 1266a33a49ea..c786e21c6051 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -1020,6 +1020,8 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin)
 	if (percpu_counter_read_positive(&vm_committed_as) < allowed)
 		return 0;
 error:
+	pr_warn_ratelimited("%s: pid: %d, comm: %s, no enough memory for the allocation\n",
+			    __func__, current->pid, current->comm);
 	vm_unacct_memory(pages);
 
 	return -ENOMEM;
-- 
2.35.3