Message-ID: <3F706046.1000306@euronext.nl>
Date: Tue, 23 Sep 2003 17:01:26 +0200
From: Jan Evert van Grootheest <j.grootheest@euronext.nl>
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To: Andrea Arcangeli <andrea@suse.de>
CC: Willy Tarreau <willy@w.ods.org>,
       Marcelo Tosatti <marcelo.tosatti@cyclades.com.br>,
       linux-kernel@vger.kernel.org
Subject: Re: log-buf-len dynamic
References: <20030922194833.GA2732@velociraptor.random> <20030923042855.GF589@alpha.home.local> <20030923124951.GB23111@velociraptor.random> <20030923140647.GB3113@alpha.home.local> <20030923144435.GC23111@velociraptor.random>
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Andrea,

since you ask...
I consider myself a not very typical Linux user in that I am a 
programmer too and I (sometimes) write programs for Linux as well. And 
yes, I do compile my own kernels.

I think it is pretty senseless to have a configuation option for the 
default size of that buffer. Especially if I can, in one of the first rc 
scripts, do something like 'echo 128 > /proc/sys/kernel/printkbuffer'.
The only hard requirement for that default size is that all output up 
till that rc script fits into a buffer of that size.

And yes, I do care about that static 64K buffer. I still have an old 
pentium that only has 16M. Every byte counts!

On the other hand there are the really large systems with many CPUs and 
such. Those might have problems with the small default. But, well, those 
really could #ifdef a different default based on some configuration 
options...

-- Jan Evert

Andrea Arcangeli wrote:

> On Tue, Sep 23, 2003 at 04:06:47PM +0200, Willy Tarreau wrote:
> 
>>Hi Andrea,
>> 
>>
>>>The point here is that the default must work for 99% of the userbase.
>>>Either that or the default is totally broken.
>>
>>You're only thinking about what distro vendors should do. If all kernels should
>>suit their needs, then there would not be any config anymore, and everyone
>>would have the same kernel with the same wagon of command line arguments.
> 
> 
> this is actually not true. Many options are way too costly to recompile
> every time, or to keep enabled at runtime, it can't be the case for this
> one. My own self compiled kernel has a very stripped down .config, it's
> not like a distro kernel with everything included.
> 
> 
>>I said I agree on the dynamic advantage. BTW, you didn't reply me about what
>>the statically allocated 64 kB became with your patch. Will this memory be
> 
> 
> the 64k are wasted only when you use the option, if you need more than
> 64k it's unlikely you care about 64k lost. But I'm ok to fix it, it just
> looks a low priority to fix. Also since you will never use this option
> anyways since you don't like adding parameters to the kernel, then you
> don't care about fixing it either, you simply want the additional config
> option on top of this.
> 
> My whole argument is that being able to do it dynamic is an order of
> magnitude more important than being able to do it statically, no matter
> the command line argument and no matter ther 64k lost. You must agree
> with that. the amount of userbase is just not comparable.
> 
> 
>>wasted forever or is there a way to free it ? If I want to pre-allocate it
>>dynamically with alloc_space() as you did, what can I use to free it ? is
>>kfree() the right thing ?
> 
> 
> we should simply allocate it from the bootmem pool, it's trivial to
> change it so the 64k aren't lost.
> 
> Not sure what I should do, personally I consider the additional .config
> option as configuration pollution, but since you care that much I can
> also change my patch not to reject yours, and to allow the two things to
> coexist, but I don't think it's really needed. I believe people should
> be forced to use the kernel params, and it's much more manageable to
> know all the kernels behave the same if no param is passed (otherwise
> you have to check the System.map to see how big the buffer is, to know
> if this was the right or wrong kernel during your remote maintainance,
> either that or you should check /proc/config.gz if you have it). It's
> just a mess if each kernel with the same revision number behaves
> differently, everything becomes less and less predictable. The number of
> System.map checks increases and increases before I can identify what
> kernel is that. Is there anybody else that has opinions on the matter?
> 
> Andrea - If you prefer relying on open source software, check these links:
> 	    rsync.kernel.org::pub/scm/linux/kernel/bkcvs/linux-2.[45]/
> 	    http://www.cobite.com/cvsps/
> 	    svn://svn.kernel.org/linux-2.[46]/trunk
> -
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