Message-ID: <54EE18DF.2040201@gmx.de>
Date: Wed, 25 Feb 2015 19:47:59 +0100
From: Heinrich Schuchardt <xypron.glpk@gmx.de>
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To: David Rientjes <rientjes@google.com>
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, Jonathan Corbet <corbet@lwn.net>
Subject: Re: [PATCH 3/3] kernel/sysctl.c: threads-max observe limits
References: <1424722477-23758-1-git-send-email-xypron.glpk@gmx.de> <1424806701-30099-1-git-send-email-xypron.glpk@gmx.de> <1424806701-30099-4-git-send-email-xypron.glpk@gmx.de> <alpine.DEB.2.10.1502241315250.3855@chino.kir.corp.google.com> <54ECED97.5070500@gmx.de> <alpine.DEB.2.10.1502241419070.11324@chino.kir.corp.google.com>
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On 24.02.2015 23:20, David Rientjes wrote:
> 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.

Hello David,

I guess the documentation fix should be put into a separate patch (of
the same patch series) as Jonathan Corbet uses a separate git tree to
consolidate documentation changes. Is that ok with you?

Best regards

Heinrich
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