linux-kernel - Re: remove zero_page (was Re: -mm merge plans for 2.6.24)

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Date:	Wed, 10 Oct 2007 08:04:29 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
cc:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: remove zero_page (was Re: -mm merge plans for 2.6.24)



On Wed, 10 Oct 2007, Nick Piggin wrote:
> 
> It just seems like now might be a good time to just _try_ removing
> the zero page

Yes. Let's do your patch immediately after the x86 merge, and just see if 
anybody screams. 

It might take a while, because I certainly agree that whoever would be 
affected by it is likely to be unusual.

> OK, maybe this is where we are not on the same page.
> There are 2 issues really. Firstly, performance problem of
> refcounting the zero-page -- we've established that it causes
> this livelock and that we should stop refcounting it, right?

Yes, I do agree that refcounting is problematic. 

> Second issue is the performance difference between removing the
> zero page completely, and de-refcounting it (it's obviously
> incorrect to argue for zero page removal for performance reasons
> if the performance improvement is simply coming from avoiding
> the refcounting).

Well, even if it's a "when you don't get into the bad behaviour, 
performance difference is not measurable", and give a before-and-after 
number for some random but interesting load. Even if it's just a kernel 
compile..

		Linus
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