[PATCH] mm, tracing: record slab name for kmem_cache_free()

[Jacob Wen <jian.w.wen@xxxxxxxxxx>]

Currently, a trace record generated by the RCU core is as below.

... kmem_cache_free: call_site=rcu_core+0x1fd/0x610 ptr=00000000f3b49a66

It doesn't tell us what the RCU core has freed.

This patch adds the slab name to trace_kmem_cache_free().
The new format is as follows.

... kmem_cache_free: call_site=rcu_core+0x1fd/0x610 ptr=0000000037f79c8d name=dentry
... kmem_cache_free: call_site=rcu_core+0x1fd/0x610 ptr=00000000f78cb7b5 name=sock_inode_cache
... kmem_cache_free: call_site=rcu_core+0x1fd/0x610 ptr=0000000018768985 name=pool_workqueue
... kmem_cache_free: call_site=rcu_core+0x1fd/0x610 ptr=000000006a6cb484 name=radix_tree_node

We can use it to understand what the RCU core is going to free. For
example, some users maybe interested in when the RCU core starts
freeing reclaimable slabs like dentry to reduce memory pressure.

Signed-off-by: Jacob Wen <jian.w.wen@xxxxxxxxxx>
---
 include/trace/events/kmem.h | 24 ++++++++++++++++--------
 mm/slab.c                   |  2 +-
 mm/slob.c                   |  2 +-
 mm/slub.c                   |  2 +-
 4 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/include/trace/events/kmem.h b/include/trace/events/kmem.h
index f65b1f6db22d..40845b0d5dad 100644
--- a/include/trace/events/kmem.h
+++ b/include/trace/events/kmem.h
@@ -115,7 +115,7 @@ DEFINE_EVENT(kmem_alloc_node, kmem_cache_alloc_node,
 	TP_ARGS(call_site, ptr, bytes_req, bytes_alloc, gfp_flags, node)
 );
 
-DECLARE_EVENT_CLASS(kmem_free,
+TRACE_EVENT(kfree,
 
 	TP_PROTO(unsigned long call_site, const void *ptr),
 
@@ -135,18 +135,26 @@ DECLARE_EVENT_CLASS(kmem_free,
 		  (void *)__entry->call_site, __entry->ptr)
 );
 
-DEFINE_EVENT(kmem_free, kfree,
+TRACE_EVENT(kmem_cache_free,
 
-	TP_PROTO(unsigned long call_site, const void *ptr),
+	TP_PROTO(unsigned long call_site, const void *ptr, const char *name),
 
-	TP_ARGS(call_site, ptr)
-);
+	TP_ARGS(call_site, ptr, name),
 
-DEFINE_EVENT(kmem_free, kmem_cache_free,
+	TP_STRUCT__entry(
+		__field(	unsigned long,	call_site	)
+		__field(	const void *,	ptr		)
+		__field(	const char *,	name		)
+	),
 
-	TP_PROTO(unsigned long call_site, const void *ptr),
+	TP_fast_assign(
+		__entry->call_site	= call_site;
+		__entry->ptr		= ptr;
+		__entry->name		= name;
+	),
 
-	TP_ARGS(call_site, ptr)
+	TP_printk("call_site=%pS ptr=%p name=%s",
+		  (void *)__entry->call_site, __entry->ptr, __entry->name)
 );
 
 TRACE_EVENT(mm_page_free,
diff --git a/mm/slab.c b/mm/slab.c
index d7c8da9319c7..f35d395794bd 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3697,7 +3697,7 @@ void kmem_cache_free(struct kmem_cache *cachep, void *objp)
 	__cache_free(cachep, objp, _RET_IP_);
 	local_irq_restore(flags);
 
-	trace_kmem_cache_free(_RET_IP_, objp);
+	trace_kmem_cache_free(_RET_IP_, objp, cachep->name);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
diff --git a/mm/slob.c b/mm/slob.c
index 8d4bfa46247f..ffb34600b48c 100644
--- a/mm/slob.c
+++ b/mm/slob.c
@@ -667,7 +667,7 @@ void kmem_cache_free(struct kmem_cache *c, void *b)
 		__kmem_cache_free(b, c->size);
 	}
 
-	trace_kmem_cache_free(_RET_IP_, b);
+	trace_kmem_cache_free(_RET_IP_, b, c->name);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
diff --git a/mm/slub.c b/mm/slub.c
index 4552319148f6..5c28d8721430 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3154,7 +3154,7 @@ void kmem_cache_free(struct kmem_cache *s, void *x)
 	if (!s)
 		return;
 	slab_free(s, virt_to_head_page(x), x, NULL, 1, _RET_IP_);
-	trace_kmem_cache_free(_RET_IP_, x);
+	trace_kmem_cache_free(_RET_IP_, x, s->name);
 }
 EXPORT_SYMBOL(kmem_cache_free);
 
-- 
2.17.1