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Date:      Fri, 22 Jan 2016 12:09:40 +0000
From:      David Chisnall <theraven@FreeBSD.org>
To:        Ed Maste <emaste@freebsd.org>
Cc:        =?utf-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>, FreeBSD Current <freebsd-current@freebsd.org>
Subject:   Re: Too low PTHREAD_STACK_MIN value?
Message-ID:  <E2C880CC-10A1-40A0-8489-68C6A8DF27F9@FreeBSD.org>
In-Reply-To: <CAPyFy2BK6R90pop9v_%2BtW54cv3BoHCQkxBu4-E2fnZ1BptsfHw@mail.gmail.com>
References:  <531F42CD.8020307@citrix.com> <913B1E7A-5192-430F-ABAF-576DFCFF98E6@FreeBSD.org> <CAPyFy2BK6R90pop9v_%2BtW54cv3BoHCQkxBu4-E2fnZ1BptsfHw@mail.gmail.com>

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On 21 Jan 2016, at 16:02, Ed Maste <emaste@freebsd.org> wrote:
>=20
> I found that lang/polyml uses PTHREAD_STACK_MIN for a trivial signal
> handler thread it creates[1]. They found it was too small and
> implemented a 4K minimum bound to fix polyml on FreeBSD[2]. Even if
> this isn't really the intended use of PTHREAD_STACK_MIN it suggests
> the 2K x86 minimum may indeed be too low.
>=20
> I ran into this while trying LLVM's libunwind, which requires more
> stack space. 2K is certainly too low with LLVM libunwind. Is it
> reasonable to just increase it to say 8K?

I don=E2=80=99t really like this solution.  PTHREAD_STACK_MIN is the =
size for a stack that does not do anything.  You should never use it =
without adding the amount that you are going to need (which might be =
nothing if you are running code from a language that does not use a =
conventional C-style stack, but still wants to use OS threads).  Making =
it larger because a specific kind of thing that some consumers want to =
do with it needs more space is definitely against the spirit of the =
value and potentially harmful as it means that people using it correctly =
will be using a lot more memory per thread.

David




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