Re: [PATCH] mm: Always sanity check anon_vma first for per-vma locks

[Matthew Wilcox]

On Wed, Apr 10, 2024 at 05:23:18PM -0400, Peter Xu wrote:
> On Wed, Apr 10, 2024 at 10:10:45PM +0100, Matthew Wilcox wrote:
> > > I can do some tests later today or tomorrow. Any suggestion you have on
> > > amplifying such effect that you have concern with?
> > 
> > 8 socket NUMA system, 800MB text segment, 10,000 threads.  No, I'm not
> > joking, that's a real customer workload.
> 
> Well, I believe you, but even with this, that's a total of 800MB memory on
> a giant moster system... probably just to fault in once.
> 
> And even before we talk about that into details.. we're talking about such
> giant program running acorss hundreds of cores with hundreds of MB text,
> then... hasn't the program developer already considered mlockall() at the
> entry of the program?  Wouldn't that greatly beneficial already with
> whatever granule of locks that a future fault would take?

I don't care what your theory is, or even what your benchmarking shows.
I had basically the inverse of this patch, and my customer's workload
showed significant improvement as a result.  Data talks, bullshit walks.
Your patch is NAKed and will remain NAKed.