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Date: Sat, 7 May 2016 10:45:57 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Darren Hart <dvhart@infradead.org>
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        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>,
        "Carlos O'Donell" <carlos@redhat.com>,
        Torvald Riegel <triegel@redhat.com>,
        Eric Dumazet <edumazet@google.com>
Subject: Re: [patch V2 2/7] futex: Hash private futexes per process
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On Fri, 6 May 2016, Darren Hart wrote:
 > It would be good to have a way to detect that the process private hash table was
> > successfully created. Perhaps a /proc/pid/ feature? This would allow us to write
> > a functional futex test for tools/testing/selftests/futex
> 
> I suppose we could just use FUTEX_PREALLOC_HASH for this purpose, passing in the
> default hash size. This will either return the default, the previously set
> value, or 0, indicating the global hash is being used. That should be sufficient
> for programatically determining the state of the system.

Right.
 
> The /proc/pid/futex_hash_size option may still be convenient for other purposes.
> Perhaps with a -1 indicating it hasn't been set yet.

Dunno, whether that's valuable, but it can be done on top.

Thanks,

	tglx