Re: [patch 014/173] mm, tracing: record slab name for kmem_cache_free()

From: Jacob Wen <redacted>
Subject: mm, tracing: record slab name for kmem_cache_free()

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.

Link: https://lkml.kernel.org/r/20201216072804.8838-1-jian.w.wen@oracle.com
Signed-off-by: Jacob Wen <redacted>
Cc: Christoph Lameter <redacted>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <redacted>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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(-)

--- a/include/trace/events/kmem.h~mm-tracing-record-slab-name-for-kmem_cache_free
+++ a/include/trace/events/kmem.h

@@ -115,7 +115,7 @@ DEFINE_EVENT(kmem_alloc_node, kmem_cache
 	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,

--- a/mm/slab.c~mm-tracing-record-slab-name-for-kmem_cache_free
+++ a/mm/slab.c

@@ -3717,7 +3717,7 @@ void kmem_cache_free(struct kmem_cache *
 	__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);
 
--- a/mm/slob.c~mm-tracing-record-slab-name-for-kmem_cache_free
+++ a/mm/slob.c

@@ -673,7 +673,7 @@ void kmem_cache_free(struct kmem_cache *
 		__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);
 
--- a/mm/slub.c~mm-tracing-record-slab-name-for-kmem_cache_free
+++ a/mm/slub.c

@@ -3157,7 +3157,7 @@ void kmem_cache_free(struct kmem_cache *
 	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);
 

_