linux-kernel - Re: [RFC][PATCH 2/2] kernel: extract thread types from task

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Date:	Mon, 20 Sep 2010 21:25:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Tejun Heo <tj@...nel.org>, Avi Kivity <avi@...hat.com>
Subject: Re: [RFC][PATCH 2/2] kernel: extract thread types from
 task_struct::flags

On Mon, 2010-09-20 at 12:14 -0700, Andrew Morton wrote:
> On Mon, 20 Sep 2010 17:13:36 +0200
> Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> > Free up a few more PF_flags by moving thread types out to their own variable.
> > 
> > Initially I compressed the types into less bits inside task_struct::flags, but
> > Thomas suggested I move them to their own field.
> > 
> 
> There doesn't seem to be a huge point to all this, but I guess there's
> some sense in separating "what type of thread this is" from "attributes
> of this thread".  Maybe.  At the expense of a larger task_struct. 

Yeah, with the PF_FLUSHER and PF_ALIGNWARN things removed we again have
2 bits free in flags.

And that's the amount -rt consumes (it adds 2 more: I'm a $FOO thread,
flags).

But having looked at it, I came up with the compress I'm a $FOO thread,
idea. Which would free up a few more bits for future use.

At that time Thomas suggested I move it into a separate field, and then
Linus said, don't compact the types, simply transfer the bits we have.

Anyway, it was all very much RFC.. and comments I got :-)

So can you agree with Linus' proposal of simply moving all type like
bits over to a new word, or would you rather see the linear type field
with an extra helper; possibly part of the existing ->flags field?

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