linux-kernel - Re: [PATCH 06/11] IMA: use i_writecount rather than a private counter

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Message-ID: <4CC603E3.3070405@zytor.com>
Date:	Mon, 25 Oct 2010 15:25:39 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Eric Paris <eparis@...hat.com>
CC:	John Stoffel <john@...ffel.org>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, hch@...radead.org, zohar@...ibm.com,
	warthog9@...nel.org, david@...morbit.com, jmorris@...ei.org,
	kyle@...artin.ca, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, mingo@...e.hu,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH 06/11] IMA: use i_writecount rather than a private counter

On 10/25/2010 02:52 PM, Eric Paris wrote:
> On Mon, 2010-10-25 at 15:27 -0400, John Stoffel wrote:
> 
>> The problems with kernel.org is a perfect exmaple of how an annocuous
>> feature like this, can kill a system's performance.
> 
> You admit that you don't know what you are talking about and then state
> that this kills systems performance.  Interesting conclusion.
> 
> I'm not going to try to refute you point by point but will instead paint
> a broad picture.  I see 3 possible states:
> 1) Configured out - 0 overhead.  period.
> 2) Configured in but default disabled
> 3) Configured in and enabled by admin intervention
> 
> I have (I think) pretty clearly discussed the overhead and the changes
> made in case #2.  We expand struct inode by 4 bytes, we increment and
> decrement those 4 bytes on open/close() and we use a new inode->i_flags.
> 

Case #2 is the bad one, as long as distros are likely to compile it in.

	-hpa
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