Re: [patch 0/5] Support for sanitization flag in low-level page allocator

Ingo Molnar
2009-05-30T22:10:27Z

* Rik van Riel <riel@redhat.com> wrote:

> Ingo Molnar wrote:
>> * Larry H. <research@subreption.com> wrote:
>>> On 20:21 Sat 30 May , Ingo Molnar wrote:
>
>>>> Freeing keys is an utter slow-path (if not then the clearing is
>>>> the least of our performance worries), so any clearing cost is in
>>>> the noise. Furthermore, kzfree() is an existing facility already in
>>>> use. If it's reused by your patches that brings further advantages:
>>>> kzfree(), if it has any bugs, will be fixed. While if you add a
>>>> parallel facility kzfree() stays broken.
>>> Have you benchmarked the addition of these changes? I would like to
>>> see benchmarks done for these (crypto api included), since you are
>>> proposing them.
>>
>> You have it the wrong way around. _You_ have the burden of proof here
>> really, you are trying to get patches into the upstream kernel. I'm not
>> obliged to do your homework for you. I might be wrong, and you can
>> prove me wrong.
>
> Larry's patches do not do what you propose they should do, so why
> would he have to benchmark your idea?

My (and AFAICT Pekka's) suggestion was to use unconditional kzfree()
in the few places where it matters: crypto/WEP key and input stream
freeing.

His counter-argument was that it is unacceptable overhead - without
any supporting data. I dont think the overhead is a problem in those
cases (without any supporting data either).

Obviously the argument is best settled by measurements. Done by
whoever wants to push this code.

Ingo