This patch prints the status of the memory allocation profiling
before __show_mem actually prints the detailed allocation info.
This way will let us know the `0B` we saw in allocation info is
because the profiling is disabled or the allocation is actually
0B.

Signed-off-by: Yueyang Pan <pyyjason@gmail.com>
---
 mm/show_mem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index ecf20a93ea54..51892ce2efc4 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -427,6 +427,8 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 
 		nr = alloc_tag_top_users(tags, ARRAY_SIZE(tags), false);
 		if (nr) {
+			pr_notice("Memory alloction profiling is turned %s\n",
+				mem_alloc_profiling_enabled() ? "on" : "off");
 			pr_notice("Memory allocations:\n");
 			for (i = 0; i < nr; i++) {
 				struct codetag *ct = tags[i].ct;
-- 
2.47.3


In production, show_mem() can be called concurrently from two
different entities, for example one from oom_kill_process()
another from __alloc_pages_slowpath from another kthread. This
patch adds a spinlock and invokes trylock before printing out the
kernel alloc info in show_mem(). This way two alloc info won't
interleave with each other, which then makes parsing easier.

Signed-off-by: Yueyang Pan <pyyjason@gmail.com>
---
 mm/show_mem.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/show_mem.c b/mm/show_mem.c
index 51892ce2efc4..4c876ea2b66f 100644
--- a/mm/show_mem.c
+++ b/mm/show_mem.c
@@ -396,6 +396,7 @@ static void show_free_areas(unsigned int filter, nodemask_t *nodemask, int max_z
 
 void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 {
+	static DEFINE_SPINLOCK(mem_alloc_profiling_spinlock);
 	unsigned long total = 0, reserved = 0, highmem = 0;
 	struct zone *zone;
 
@@ -421,7 +422,7 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 	printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages));
 #endif
 #ifdef CONFIG_MEM_ALLOC_PROFILING
-	{
+	if (spin_trylock(&mem_alloc_profiling_spinlock)) {
 		struct codetag_bytes tags[10];
 		size_t i, nr;
 
@@ -449,6 +450,7 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx)
 						  ct->lineno, ct->function);
 			}
 		}
+		spin_unlock(&mem_alloc_profiling_spinlock);
 	}
 #endif
 }
-- 
2.47.3