linux-kernel - Re: [PATCH 0/4] futex: get_user_pages

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Message-Id: <200809301721.52148.nickpiggin@yahoo.com.au>
Date:	Tue, 30 Sep 2008 17:21:51 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Eric Dumazet <dada1@...mosbay.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 0/4] futex: get_user_pages_fast() for shared futexes

On Sunday 28 September 2008 02:17, Ingo Molnar wrote:
> * Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> > Since get_user_pages_fast() made it in, I thought to give this another
> > try. Lightly tested by disabling the private futexes and running some
> > java proglets.
>
> hm, very interesting. Since this is an important futex usecase i started
> testing it in tip/core/futexes:
>
>  cd33272: futex: cleanup fshared
>  a135356: futex: use fast_gup()
>  39ce77b: futex: reduce mmap_sem usage
>  0d7a336: futex: rely on get_user_pages() for shared futexes
>
> Nick, it would be nice to get an Acked-by/Reviewed-by from you, before
> we think about whether it should go upstream.

Yeah, these all look pretty good. It's nice to get rid of mmap sem here.

Which reminds me, we need to put a might_lock mmap_sem into
get_user_pages_fast...

But these patches look good to me (last time we discussed them I thought
there was a race with page truncate, but it looks like you've closed that
by holding page lock over the whole operation...)

Nice work, Peter.

BTW. what kinds of things use inter-process futexes as of now?
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