linux-kernel - Re: [PATCH 1/3] IMA: move read/write counters into struct inode

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Date:	Wed, 20 Oct 2010 17:15:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric Paris <eparis@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	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, hpa@...or.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/3] IMA: move read/write counters into struct inode


* Eric Paris <eparis@...hat.com> wrote:

> On Wed, 2010-10-20 at 16:38 +0200, Ingo Molnar wrote:
> > * Eric Paris <eparis@...hat.com> wrote:
> > 
> > > Executive summary of the day's work:
> > > Yesterday morning: 944 bytes per inode in core
> > > Yesterday night: 24 bytes per inode in core
> > > Tonight: 4 bytes per inode in core.
> > > 
> > > That's a x236 time reduction in memory usage.  No I didn't even start looking 
> > > at a freezer.  Which could bring that 4 down to 0, but would add a scalability 
> > > penalty on all inodes when IMA was enabled.
> > 
> > Why not use inode->i_security intelligently? That already exists so that way 
> > it's 0 bytes.
> > 
> > Thanks,
> 
> It still wouldn't be 0 bytes since there would be a 1-1 mapping from inode to 
> i_security structs. [...]

Only for IMA-affected files, right?

My point is to keep it 0 overhead for the _non IMA common case_.

> The real reason I don't pursue this route is because of the litany of different 
> ways this pointer is used in different LSMs (or not used at all.)  And we all know 
> that LSM authors aren't known for seeing the world the same way as each other.  As 
> a maintainer of one of those LSMs even I'm scared to try pushing that forward....

Ugh. That's a perfect reason to do it exactly like i suggested.

Thanks,

	Ingo
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