Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)

[Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>]

On Thu, Apr 12, 2018 at 12:59 PM, Mathieu Desnoyers
<mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>
> What are your concerns about page pinning ?

Pretty much everything.

It's the most complex part by far, and the vmalloc space is a limited
resource on 32-bit architectures.

> Do you have an alternative approach in mind ?

Do everything in user space.

And even if you absolutely want cpu_opv at all, why not do it in the
user space *mapping* without the aliasing into kernel space?

The cpu_opv approach isn't even fast. It's *really* slow if it has to
do VM crap.

The whole rseq thing was billed as "faster than atomics". I
*guarantee* that the cpu_opv's aren't faster than atomics.

                 Linus