Re: [RFC] perf: mmap2 not covering VM_CLONE regions

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Oct 03, 2013 at 10:55:28AM +0200, Stephane Eranian wrote:
> I don't know the MM code but I assume that that vm_mm struct is
> allocated dynamically
> and maybe you already grabbing a lock while doing this. Could we
> leverage that lock
> to increment a global generation number?

Sure; something like so.. I just don't like global state nor adding to
mm_struct for just this.

---
 include/linux/mm_types.h | 1 +
 kernel/fork.c            | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index d9851eeb6e1d..3877b1e72a5b 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -436,6 +436,7 @@ struct mm_struct {
 	int first_nid;
 #endif
 	struct uprobes_state uprobes_state;
+	u64 mm_id;
 };
 
 /* first nid will either be a valid NID or one of these values */
diff --git a/kernel/fork.c b/kernel/fork.c
index 086fe73ad6bd..b315f6227629 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -523,6 +523,8 @@ static void mm_init_aio(struct mm_struct *mm)
 #endif
 }
 
+static u64 global_mm_id;
+
 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 {
 	atomic_set(&mm->mm_users, 1);
@@ -537,6 +539,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)
 	spin_lock_init(&mm->page_table_lock);
 	mm_init_aio(mm);
 	mm_init_owner(mm, p);
+	mm->mm_id = 0;
 
 	if (likely(!mm_alloc_pgd(mm))) {
 		mm->def_flags = 0;
@@ -1422,6 +1425,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	 */
 	write_lock_irq(&tasklist_lock);
 
+	if (p->mm && !p->mm->mm_id)
+		p->mm->mm_id = ++global_mm_id;
+
 	/* CLONE_PARENT re-uses the old parent */
 	if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
 		p->real_parent = current->real_parent;