Date: Tue, 24 Feb 2015 14:20:04 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Heinrich Schuchardt <xypron.glpk@gmx.de>
cc: Andrew Morton <akpm@linux-foundation.org>,
        Aaron Tomlin <atomlin@redhat.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Davidlohr Bueso <dave@stgolabs.net>,
        "David S. Miller" <davem@davemloft.net>,
        Fabian Frederick <fabf@skynet.be>, Guenter Roeck <linux@roeck-us.net>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@kernel.org>,
        Jens Axboe <axboe@fb.com>, Joe Perches <joe@perches.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Kees Cook <keescook@chromium.org>,
        Michael Marineau <mike@marineau.org>, Oleg Nesterov <oleg@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Prarit Bhargava <prarit@redhat.com>, Rik van Riel <riel@redhat.com>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vladimir Davydov <vdavydov@parallels.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] kernel/sysctl.c: threads-max observe limits
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On Tue, 24 Feb 2015, Heinrich Schuchardt wrote:

> >> Users can change the maximum number of threads by writing to
> >> /proc/sys/kernel/threads-max.
> >>
> >> With the patch the value entered is checked against the same
> >> limits that apply when fork_init is called.
> >>
> > 
> > Correct me if I'm wrong, but this is a change in functionality (without 
> > update to Documentation/sysctl/kernel.txt which describes threads-max) 
> > since it does not allow the value to be lowered as before from the 
> > calculation involving totalram_pages.  The value passed to 
> > set_max_threads() only caps the value.
> 
> threads_max is set to the value the user inputs if it is inside the
> interval [20, FUTEX_TID_MASK] and it is capped by the value calculated
> from totalram_pages.
> 
> So lowering and raising is still possible (inside the limits).
> 

I believe this information should be added to the documentation cited 
above which mentions threads-max since users will otherwise be unfamiliar 
with the limits imposed.
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