linux-kernel - Re: [RFC][PATCH 6/6] automatic tuning applied to some kernel components

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Date:	Tue, 13 Feb 2007 10:06:21 +0100
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 6/6] automatic tuning applied to some kernel components

Eric W. Biederman wrote:
> Nadia Derbey <Nadia.Derbey@...l.net> writes:
> 
> 
>>I do not fully agree with you:
>>It is true that some ipc tunables play the role of DoS limits.
>>But IMHO the *mni ones (semmni, msgmni, shmmni) are used by the ipc subsystem to
>>adapt its data structures sizes to what is being asked for through the tunable
>>value. I think this is how they manage to take into account a new tunable value
>>without a need for rebooting the system: reallocate some more memory on demand.
> 
> 
> Yes, they do.  However if you are constantly having to play with shmmni or
> the others that is the problem and the array should be replaced with
> a hash table or some form of radix tree, so it changes it's size to fit
> the need.  Once that is done, shmmni does become a simple DOS limit.
> 
> So what I'm asking is please fix the problem at the source don't plaster over
> it.
> 
> 
>>Now, what the akt framework does, is that it takes advantage of this concept of
>>"on demand memory allocation" to replace a user (or a daemon) that would
>>periodically check its ipcs consumptions and manually adjust the ipcs tunables:
>>Doing this from the user space would imply a latency that makes it difficult to
>>react fast enough to resources running out.
> 
> 
> There may be some sense in this but you haven't found something that inherently
> needs tuning.  You have found something that has a poor data structure,
> and can more easily be fixed by simply fixing the data structure.

So, should I understand from this that automatic tuning and the AKT 
framework itself would make sense, given that I find the rigth tunables 
it should be applied to?
Actually, dont' know if you had the opportunity to read all the patches, 
but there are 2 other tunables AKT is proposed to be applied to:
. max_threads, the tunable limit on nr_threads
. max_files, the tunable limit on nr_files

Regards,
Nadia

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