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Date:      Sat, 10 Nov 2012 09:04:48 -0800
From:      Alfred Perlstein <bright@mu.org>
To:        Eitan Adler <eadler@freebsd.org>
Cc:        svn-src-head@freebsd.org, svn-src-all@freebsd.org, Alfred Perlstein <alfred@freebsd.org>, src-committers@freebsd.org
Subject:   Re: svn commit: r242847 - in head/sys: i386/include kern
Message-ID:  <509E8930.50800@mu.org>
In-Reply-To: <CAF6rxgnfm4HURYp=O4MY8rB6H1tGiqJ3rdPx0rZ8Swko5mAOZg@mail.gmail.com>
References:  <201211100208.qAA28e0v004842@svn.freebsd.org> <CAF6rxg=HPmQS1T-LFsZ=DuKEqH30iJFpkz%2BJGhLr4OBL8nohjg@mail.gmail.com> <509DC25E.5030306@mu.org> <509E3162.5020702@FreeBSD.org> <509E7E7C.9000104@mu.org> <CAF6rxgmV8dx-gsQceQKuMQEsJ%2BGkExcKYxEvQ3kY%2B5_nSjvA3w@mail.gmail.com> <509E830D.5080006@mu.org> <509E847E.30509@mu.org> <CAF6rxgnfm4HURYp=O4MY8rB6H1tGiqJ3rdPx0rZ8Swko5mAOZg@mail.gmail.com>

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On 11/10/12 8:48 AM, Eitan Adler wrote:
> On 10 November 2012 11:44, Alfred Perlstein <bright@mu.org> wrote:
>> On 11/10/12 8:38 AM, Alfred Perlstein wrote:
>>> On 11/10/12 8:25 AM, Eitan Adler wrote:
>>>> On 10 November 2012 11:19, Alfred Perlstein <bright@mu.org> wrote:
>>>>> Please consult the svn log for this file, it's relatively clear just in
>>>>> the
>>>>> commit logs/comments.  Grep for 384/512 and look around.
>>>> Can this reasoning be added as a comment? I did grep for 384 in the log,
>>>> but
>>>> a) I didn't find the answer
>>>> b) one shouldn't have to.
>>>>
>>>>
>>> It probably could be added, but then a bunch of other people would
>>> complain about the comment being too wordy or "not in English".
>>>
>>> I will paste the relevant log messages which do explain it.  If you would
>>> like to add a comment or work on a comment that won't be criticized for
>>> being "too wordy" then we can do that together.
>>>
>>> r89769 | dillon | 2002-01-24 17:54:16 -0800 (Thu, 24 Jan 2002) | 9 lines
>>>
>>> Make the 'maxusers 0' auto-sizing code slightly more conservative. Change
>>> from 1 megabyte of ram per user to 2 megabytes of ram per user, and
>>> reduce the cap from 512 to 384.  512 leaves around 240 MB of KVM available
>>> while 384 leaves 270 MB of KVM available.  Available KVM is important
>>> in order to deal with zalloc and kernel malloc area growth.
>>>
>>> Reviewed by:    mckusick
>>> MFC: either before 4.5 if re's agree, or after 4.5
>>>
>>>
>>> r87546 | dillon | 2001-12-08 17:57:09 -0800 (Sat, 08 Dec 2001) | 6 lines
>>>
>>> Allow maxusers to be specified as 0 in the kernel config, which will
>>> cause the system to auto-size to between 32 and 512 depending on the
>>> amount of memory.
>>>
>>> MFC after:      1 week
>>>
>> Let me add a bit of commentary on these logs...
>>
>> Effectively what happens is that as "maxusers" goes up, the amount of kernel
>> memory needed for the structures grows.  Unfortunately at a certain point
>> the slope of this function is too steep and makes it too easy to exhaust
>> kernel address space (which kills the crab (and the kernel)) what was
>> decided at the time was just to cap it hard.
> I understand this. What I was confused by is where the number "384"
> comes from? Was this empirically tested? Mathematically deduced?
> Arbitrarily chosen?
>
> I think the log messages you pasted mostly answered this.
>
>
Sure, if you'd like you can help me craft that comment now?

-alfred



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