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Re: CVS commit: src/sys/kern



Nick Hudson <skrll%netbsd.org@localhost> writes:

> 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%.

I think that options(4) is buggy here.  The historical norms for
DIAGNOSTIC are nowhere near 15% being acceptable.    There is also no
notion of increasing memory usage under DIAGNOSTIC.

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