Re: [PATCH V2 2/7] mm/gup: add gup trace points

[Shi, Yang]

On 12/3/2015 11:06 AM, Steven Rostedt wrote:
> On Thu, 03 Dec 2015 10:36:18 -0800
> "Shi, Yang" <yang.shi@xxxxxxxxxx> wrote:
>
> > > called directly that calls these functions internally and the tracepoint
> > > can trap the return value.
> >
> > This will incur more changes in other subsystems (futex, kvm, etc), I'm
> > not sure if it is worth making such changes to get return value.
>
> No, it wouldn't require any changes outside of this.
>
> -long __get_user_pages(..)
> +static long __get_user_pages_internal(..)
> {
>    [..]
> }
> +
> +long __get_user_pages(..)
> +{
> +	long ret;
> +	ret = __get_user_pages_internal(..);
> +	trace_get_user_pages(.., ret)
> +}

Thanks for this. I just checked the fast version, it looks it just has 
single return path, so this should be just needed by slow version.

> > > I can probably make function_graph tracer give return values, although
> > > it will give a return value for void functions as well. And it may give
> > > long long returns for int returns that may have bogus data in the
> > > higher bits.
> >
> > If the return value requirement is not limited to gup, the approach
> > sounds more reasonable.
>
> Others have asked about it. Maybe I should do it.

If you are going to add return value in common trace code, I won't do 
the gup specific one in V3.

Thanks,
Yang

> -- Steve

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