# Re: \[RFC PATCH v3 12/24\] x86/mm: Modify ptep\_set\_wrprotect and pmdp\_set\_wrprotect for \_PAGE\_DIRTY\_SW

- From: Peter Zijlstra \<peterz@infradead.org\>
- Date: 2018-08-31 16:30:07 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2018/08/5368797
- Thread: https://ratatoskr.run/linux-doc/2018/08/5367691/t.md

```text
On Fri, Aug 31, 2018 at 08:58:39AM -0700, Dave Hansen wrote:
> On 08/31/2018 08:48 AM, Yu-cheng Yu wrote:
> > To trigger a race in ptep_set_wrprotect(), we need to fork from one of
> > three pthread siblings.
> > 
> > Or do we measure only how much this affects fork?
> > If there is no racing, the effect should be minimal.
> 
> We don't need a race.
> 
> I think the cmpxchg will be slower, even without a race, than the code
> that was there before.  The cmpxchg is a simple, straightforward
> solution, but we're putting it in place of a plain memory write, which
> is suboptimal.

Note quite, the clear_bit() is LOCK prefixed.
```