perf_event: Allocate children's perf_event_ctxp at the right time

In current code, children task will allocate memory for
'child->perf_event_ctxp' if the parent is counted, we can
do it only if the parent allowed children inherit it.

It can save memory and reduce overhead.

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Reviewed-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <4B1F19A8.5040805@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 22 insertions, 15 deletions

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 2b06c45bfba9..77641ae6b23f 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -5083,7 +5083,7 @@ again:
  */
 int perf_event_init_task(struct task_struct *child)
 {
-        struct perf_event_context *child_ctx, *parent_ctx;
+        struct perf_event_context *child_ctx = NULL, *parent_ctx;
         struct perf_event_context *cloned_ctx;
         struct perf_event *event;
         struct task_struct *parent = current;
@@ -5099,20 +5099,6 @@ int perf_event_init_task(struct task_struct *child)
                 return 0;
 
         /*
-         * This is executed from the parent task context, so inherit
-         * events that have been marked for cloning.
-         * First allocate and initialize a context for the child.
-         */
-
-        child_ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
-        if (!child_ctx)
-                return -ENOMEM;
-
-        __perf_event_init_context(child_ctx, child);
-        child->perf_event_ctxp = child_ctx;
-        get_task_struct(child);
-
-        /*
          * If the parent's context is a clone, pin it so it won't get
          * swapped under us.
          */
@@ -5142,6 +5128,26 @@ int perf_event_init_task(struct task_struct *child)
                         continue;
                 }
 
+                if (!child->perf_event_ctxp) {
+                        /*
+                         * This is executed from the parent task context, so
+                         * inherit events that have been marked for cloning.
+                         * First allocate and initialize a context for the
+                         * child.
+                         */
+
+                        child_ctx = kzalloc(sizeof(struct perf_event_context),
+                                            GFP_KERNEL);
+                        if (!child_ctx) {
+                                ret = -ENOMEM;
+                                goto exit;
+                        }
+
+                        __perf_event_init_context(child_ctx, child);
+                        child->perf_event_ctxp = child_ctx;
+                        get_task_struct(child);
+                }
+
                 ret = inherit_group(event, parent, parent_ctx,
                                              child, child_ctx);
                 if (ret) {
@@ -5170,6 +5176,7 @@ int perf_event_init_task(struct task_struct *child)
                 get_ctx(child_ctx->parent_ctx);
         }
 
+exit:
         mutex_unlock(&parent_ctx->mutex);
 
         perf_unpin_context(parent_ctx);