Re: [PATCH v10 04/14] unwind_user/deferred: Add unwind_deferred_trace()

On Wed, 18 Jun 2025 16:01:11 +0200
Peter Zijlstra [off-list ref] wrote:

On Tue, Jun 10, 2025 at 08:54:25PM -0400, Steven Rostedt wrote:

quoted

+#define UNWIND_MAX_ENTRIES 512  

The reason this is 512 is so that you end up with a whole page below?

Possibly. We could probably even make that configurable. Perhaps just use
sysctl_perf_event_max_contexts_per_stack ?


Josh, any comments about why you picked this number?

-- Steve

quoted

+int unwind_deferred_trace(struct unwind_stacktrace *trace)
+{
+	struct unwind_task_info *info = &current->unwind_info;
+
+	/* Should always be called from faultable context */
+	might_fault();
+
+	if (current->flags & PF_EXITING)
+		return -EINVAL;
+
+	if (!info->entries) {
+		info->entries = kmalloc_array(UNWIND_MAX_ENTRIES, sizeof(long),
+					      GFP_KERNEL);