Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM

[Michal Hocko <mhocko@kernel.org>]

On Mon 23-04-18 10:24:02, Mikulas Patocka wrote:
[...]

I am not going to comment on your continuous accusations. We can discuss
patches but general rants make very limited sense.
 
> > > > I already said that we can change it from CONFIG_DEBUG_VM to 
> > > > CONFIG_DEBUG_SG - or to whatever other option you may want, just to make 
> > > > sure that it is enabled in distro debug kernels by default.
> > > 
> > > Yes, and I think that's the right idea.  So send a v2 and ignore the
> > > replies that are clearly relating to an earlier version of the patch.
> > > Not everybody reads every mail in the thread before responding to one they
> > > find interesting.  Yes, ideally, one would, but sometimes one doesn't.
> > 
> > And look here. This is yet another ad-hoc idea. We have many users of
> > kvmalloc which have no relation to SG, yet you are going to control
> > their behavior by CONFIG_DEBUG_SG? No way! (yeah evil again)
> 
> Why aren't you constructive and pick up pick up the CONFIG flag?

Because config doesn't make that much of a sense. You do not want a
permanent vmalloc fallback unconditionally. Debugging option which
changes the behavior completely is not useful IMNHO. Besides that who is
going to enable it?

> > Really, we have a fault injection framework and this sounds like
> > something to hook in there.
> 
> The testing people won't set it up. They install the "kernel-debug" 
> package and run the tests in it.
> 
> If you introduce a hidden option that no one knows about, no one will use 
> it.

then make sure people know about it. Fuzzers already do test fault
injections.
-- 
Michal Hocko
SUSE Labs