[PATCH] mm/slub: use stackdepot to save stack trace in objects

[glittao@gmail.com]

From: Oliver Glitta <glittao@gmail.com>

Many stack traces are similar so there are many similar arrays.
Stackdepot saves each unique stack only once.

Replace field addrs in struct track with depot_stack_handle_t handle.
Use stackdepot to save stack trace.

The benefits are smaller memory overhead and possibility to aggregate
per-cache statistics in the future using the stackdepot handle
instead of matching stacks manually.

Signed-off-by: Oliver Glitta <glittao@gmail.com>
---
 init/Kconfig |  1 +
 mm/slub.c    | 79 ++++++++++++++++++++++++++++++++--------------------
 2 files changed, 50 insertions(+), 30 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 37a17853433a..a4ed2daa6c41 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1891,6 +1891,7 @@ config SLUB_DEBUG
 	default y
 	bool "Enable SLUB debugging support" if EXPERT
 	depends on SLUB && SYSFS
+	select STACKDEPOT if STACKTRACE_SUPPORT
 	help
 	  SLUB has extensive debug support features. Disabling these can
 	  result in significant savings in code size. This also disables
diff --git a/mm/slub.c b/mm/slub.c
index 9c0e26ddf300..4b18499726eb 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -35,6 +35,7 @@
 #include <linux/prefetch.h>
 #include <linux/memcontrol.h>
 #include <linux/random.h>
+#include <linux/stackdepot.h>
 
 #include <trace/events/kmem.h>
 
@@ -203,8 +204,8 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
 #define TRACK_ADDRS_COUNT 16
 struct track {
 	unsigned long addr;	/* Called from address */
-#ifdef CONFIG_STACKTRACE
-	unsigned long addrs[TRACK_ADDRS_COUNT];	/* Called from address */
+#ifdef CONFIG_STACKDEPOT
+	depot_stack_handle_t handle;
 #endif
 	int cpu;		/* Was running on cpu */
 	int pid;		/* Pid context */
@@ -581,22 +582,27 @@ static struct track *get_track(struct kmem_cache *s, void *object,
 	return kasan_reset_tag(p + alloc);
 }
 
+#ifdef CONFIG_STACKDEPOT
+static depot_stack_handle_t save_stack_trace(gfp_t flags)
+{
+	unsigned long entries[TRACK_ADDRS_COUNT];
+	depot_stack_handle_t handle;
+	unsigned int nr_entries;
+
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 4);
+	handle = stack_depot_save(entries, nr_entries, flags);
+	return handle;
+}
+#endif
+
 static void set_track(struct kmem_cache *s, void *object,
 			enum track_item alloc, unsigned long addr)
 {
 	struct track *p = get_track(s, object, alloc);
 
 	if (addr) {
-#ifdef CONFIG_STACKTRACE
-		unsigned int nr_entries;
-
-		metadata_access_enable();
-		nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
-					      TRACK_ADDRS_COUNT, 3);
-		metadata_access_disable();
-
-		if (nr_entries < TRACK_ADDRS_COUNT)
-			p->addrs[nr_entries] = 0;
+#ifdef CONFIG_STACKDEPOT
+		p->handle = save_stack_trace(GFP_KERNEL);
 #endif
 		p->addr = addr;
 		p->cpu = smp_processor_id();
@@ -623,14 +629,19 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time)
 
 	pr_err("%s in %pS age=%lu cpu=%u pid=%d\n",
 	       s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
-#ifdef CONFIG_STACKTRACE
+#ifdef CONFIG_STACKDEPOT
 	{
-		int i;
-		for (i = 0; i < TRACK_ADDRS_COUNT; i++)
-			if (t->addrs[i])
-				pr_err("\t%pS\n", (void *)t->addrs[i]);
-			else
-				break;
+		depot_stack_handle_t handle;
+		unsigned long *entries;
+		unsigned int nr_entries;
+
+		handle = READ_ONCE(t->handle);
+		if (!handle) {
+			pr_err("object allocation/free stack trace missing\n");
+		} else {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			stack_trace_print(entries, nr_entries, 0);
+		}
 	}
 #endif
 }
@@ -4017,18 +4028,26 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct page *page)
 	objp = fixup_red_left(s, objp);
 	trackp = get_track(s, objp, TRACK_ALLOC);
 	kpp->kp_ret = (void *)trackp->addr;
-#ifdef CONFIG_STACKTRACE
-	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
-		kpp->kp_stack[i] = (void *)trackp->addrs[i];
-		if (!kpp->kp_stack[i])
-			break;
-	}
+#ifdef CONFIG_STACKDEPOT
+	{
+		depot_stack_handle_t handle;
+		unsigned long *entries;
+		unsigned int nr_entries;
 
-	trackp = get_track(s, objp, TRACK_FREE);
-	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
-		kpp->kp_free_stack[i] = (void *)trackp->addrs[i];
-		if (!kpp->kp_free_stack[i])
-			break;
+		handle = READ_ONCE(trackp->handle);
+		if (handle) {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
+				kpp->kp_stack[i] = (void *)entries[i];
+		}
+
+		trackp = get_track(s, objp, TRACK_FREE);
+		handle = READ_ONCE(trackp->handle);
+		if (handle) {
+			nr_entries = stack_depot_fetch(handle, &entries);
+			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
+				kpp->kp_free_stack[i] = (void *)entries[i];
+		}
 	}
 #endif
 #endif
-- 
2.31.1.272.g89b43f80a5