Re: [PATCH] percpu/module resevation: change resevation size iff X86_VSMP is set

[Christopher Lameter]

On Wed, 13 Mar 2019, Barret Rhoden wrote:

> > It is very expensive. VMSP exchanges 4K segments via RDMA between servers
> > to build a large address space and run a kernel in the large address
> > space. Using smaller segments can cause a lot of
> > "cacheline" bouncing (meaning transfers of 4K segments back and forth
> > between servers).
> >
>
> Given that these are large machines, would it be OK to statically reserve 64K
> on them for modules' percpu data?

Likely.

> The bug that led me to here was from someone running on a non-VSMP machine but
> had that config set.  Perhaps we make it more clear in the Kconfig option to
> not set it on other machines.  That might make it less likely anyone on a
> non-VSMP machine pays the 64K overhead.

Right.

> Are there any other alternatives?  Not using static SRCU in any code that
> could be built as a module seems a little harsh.

Sorry this ended up in my spam folder somehow. Just fished it out.