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

[Steven Rostedt]

On Wed, 18 Jun 2025 16:01:11 +0200
Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

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

> 
> > +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);  
>