Re: CVS commit: src/sys/kern

[Nick Hudson <skrll%netbsd.org@localhost>]

On 07/22/14 12:49, Greg Troxel wrote:
> "Maxime Villard" <maxv%netbsd.org@localhost> writes:
>
> > Module Name:    src
> > Committed By:   maxv
> > Date:           Tue Jul 22 07:38:41 UTC 2014
> >
> > Modified Files:
> >         src/sys/kern: subr_kmem.c
> >
> > Log Message:
> > Enable KMEM_REDZONE on DIAGNOSTIC. It will try to catch overflows.
> >
> > No comment on tech-kern@
> I didn't see this on tech-kern (nor did I see anything about defining
> KMEM_POISON), and now that I'm aware I object.
>
> DIAGNOSTIC, by longstanding tradition, is a lightweight and not have a
> significant performance hit.  Basically it's about KASSERT of things
> that must be true.  This is changing the size of memory allocations,
> which is far more far-reaching.

options(4) says this

     options DIAGNOSTIC
     Adds code to the kernel that does internal consistency checks. 
This code
     will cause the kernel to panic if corruption of internal data 
structures
     is detected.  These checks can decrease performance up to 15%.

I'd guess that KMEM_REDZONE add much less than 15%.

Nick