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From: Nick Piggin <nickpiggin@yahoo.com.au>
Subject: Re: [aarcange@redhat.com: [PATCH] fork vs gup(-fast) fix]
Date: Tue, 17 Mar 2009 05:33:47 +1100
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Andrea Arcangeli <aarcange@redhat.com>, Ingo Molnar <mingo@elte.hu>, Nick Piggin <npiggin@novell.com>, Hugh Dickins <hugh@veritas.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, linux-mm@kvack.org
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On Tuesday 17 March 2009 05:17:02 Linus Torvalds wrote:
> On Tue, 17 Mar 2009, Nick Piggin wrote:
> > If you disregard code motion and extra argument to copy_page_range,
> > my fix is a couple of dozen lines change to existing code, plus the
> > "decow" function (which could probably share a fair bit of code
> > with do_wp_page).
> >
> > Do you dislike the added complexity of the code? Or the behaviour
> > that gets changed?
>
> The complexity. That decow thing is shit.

copying the page on fork instead of write protecting it? The code or
the idea? Code can certainly be improved...


> So is all the extra flags for no
> good reason.

Which extra flags are you referring to?


> What's your argument against "keep it simple with a single lock, and
> adding basically a single line to reuse_swap_page() to say "don't reuse
> the page if the count is elevated"?

I made them in a previous message. It depends on what callers you want
to convert I guess. I don't think vmsplice takes to the lock approach
very well though.

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