* Andrew Morton <a...@linux-foundation.org> wrote:
> On Wed, 19 Jul 2017 15:54:27 -0700 Davidlohr Bueso <d...@stgolabs.net> wrote:
>
> > On Wed, 19 Jul 2017, Andrew Morton wrote:
> >
> > >I do rather dislike these conversions from the point of view of
> > >performance overhead and general code bloat. But I seem to have lost
> > >that struggle and I don't think any of these are fastpath(?).
> >
> > Well, since we now have fd25d19 (locking/refcount: Create unchecked atomic_t
> > implementation), performance is supposed to be ok.
>
> Sure, things are OK for people who disable the feature.
So with the WIP fast-refcount series from Kees:
[PATCH v6 0/2] x86: Implement fast refcount overflow protection
I believe the robustness difference between optimized-refcount_t and
full-refcount_t will be marginal.
I.e. we'll be able to have both higher API safety _and_ performance.
> But for people who want to enable the feature we really should minimize the
> cost
> by avoiding blindly converting sites which simply don't need it: simple,
> safe,
> old, well-tested code. Why go and slow down such code? Need to apply some
> common sense here...
It's old, well-tested code _for existing, sane parameters_, until someone finds
a
decade old bug in one of these with an insane parameters no-one stumbled upon
so
far, and builds an exploit on top of it.
Only by touching all these places do we have a chance to improve things
measurably
in terms of reducing the probability of bugs.
Thanks,
Ingo
