From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rich Felker <dalias@libc.org>
Cc: linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Darren Hart <dvhart@linux.intel.com>,
Mel Gorman <mgorman@suse.de>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Greg Ungerer <gerg@uclinux.org>, Steven Miao <realmz6@gmail.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH] futex: fix shared futex operations on nommu
Date: Tue, 26 Apr 2016 18:11:07 +0200 [thread overview]
Message-ID: <20160426161107.GF8295@linutronix.de> (raw)
In-Reply-To: <20160426155344.GK21636@brightrain.aerifal.cx>
* Rich Felker | 2016-04-26 11:53:44 [-0400]:
>The whole shared futex logic is meaningless for nommu. Perhaps I
>should have written a better message, though.
>
>With MMU, shared futex keys need to identify the physical backing for
>a memory address because it may be mapped at different addresses in
>different processes (or even multiple times in the same process).
>Without MMU this cannot happen. You only have physical addresses. So
>the "private futex" behavior of using the virtual address as the key
>is always correct (for both shared and private cases) on nommu
>systems.
So using a shared futex on NOMMU does work but it would be more
efficient to always use a private futex instead.
Is this what you are saying?
>Rich
Sebastian
next prev parent reply other threads:[~2016-04-26 16:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-26 1:03 Rich Felker
2016-04-26 9:55 ` Sebastian Andrzej Siewior
2016-04-26 15:53 ` Rich Felker
2016-04-26 16:11 ` Sebastian Andrzej Siewior [this message]
2016-04-26 16:27 ` Rich Felker
2016-04-26 22:27 ` Andrew Morton
2016-04-26 22:31 ` Rich Felker
2016-04-27 13:43 ` Thomas Gleixner
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