Messages in this thread | | | Date | Thu, 20 Jul 2017 11:34:02 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount_t |
| |
* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 19 Jul 2017 15:54:27 -0700 Davidlohr Bueso <dave@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
| |