Re: [RFC PATCH for 4.18 12/23] cpu_opv: Provide cpu_opv system call (v7)
From: Linus Torvalds
Date: Thu Apr 12 2018 - 16:07:23 EST
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