Re: [PATCH hazptr 4/4] hazptr: Introduce "try acquire" fast path, fallback to overflow list

[Boqun Feng <boqun@kernel.org>]

On Sun, Sep 27, 2026 at 01:15:39PM -0400, Mathieu Desnoyers wrote:
[...]
> > > With this change, the scan on per-CPU slots don't need to expect a
> > > wildcard anymore, because none can be produced by readers. Wildcards are
> > > only expected within overflow lists.
> > > 
> > 
> > Ok, I was missing something, but I think it's better to call it out.
> > Wildcards can only exist in the overflow lists when the context is not
> > preemptible. In other words, there won't be a preempted readers blocking
> > the synchronize_hazptr() with a wilcard in the overflow list.
> 
> Exactly ! Wildcard slots only exist during the short time-frame of the
> preempt-off read-side code region (few instructions). And with this
> patch, this does not even happen very often, because the fast path don't
> rely on the wildcards.
> 
> > 
> > So no more design trade-off question from me :)
> > 
> 
> Are you sure ? Scrolling down....
> 

I do feel with scan thread support and call_hazptr() support, we will
need to tweak the design and implementation some more, but right now it
does look good to me :)

Regards,
Boqun

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