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

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Date:	Sun, 31 May 2009 00:10:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rik van Riel <riel@...hat.com>
Cc:	"Larry H." <research@...reption.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...l.org>,
	linux-mm@...ck.org, Ingo Molnar <mingo@...hat.com>,
	pageexec@...email.hu,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page
	allocator


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

> Ingo Molnar wrote:
>> * Larry H. <research@...reption.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
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