linux-kernel - Re: [PATCH 14/38] Remove struct mm_struct::exe

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Message-Id: <20090531165026.376a914c.akpm@linux-foundation.org>
Date:	Sun, 31 May 2009 16:50:26 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexey Dobriyan <adobriyan@...il.com>,
	Matt Helsley <matthltc@...ibm.com>, xemul@...allels.com,
	containers@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, dave@...ux.vnet.ibm.com,
	mingo@...e.hu
Subject: Re: [PATCH 14/38] Remove struct mm_struct::exe_file et al

On Sun, 31 May 2009 16:15:50 -0700 (PDT) Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Sun, 31 May 2009, Andrew Morton wrote:
> > 
> > What I always find a bit weird is that an MM container is used as the
> > central point for a number of sched obects.  But it's logical, given
> > that the never-before-stated definition of a heavyweight process is
> > "thing which share a VM".
> 
> It has nothing to do with "heavy-weight process" or anything else.
> 
> The thing is, from a scheduling standpoint, one of the primary performance 
> concerns in the TLB switch.
> 
> And there's a 1:1 relationship between TLB switch and MM container, modulo 
> the issue of kernel tasks (and those obviously "borrow" approproate MM 
> structs to avoid the switch).

That's all an obscure performance-oriented internal implementation detail.

> So it's not weird at all. It's very direct, and a very straightforward and 
> obvious relationship.

It's arbitrary!  If we were to gain more performance benefit by
aggregating processes under, say, the fs_struct then that's the way the
kernel would have been implemented.

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