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From: Nadia Derbey <>
To: "Eric W. Biederman" <>
Cc: Andrew Morton <>,
Subject: Re: [RFC][PATCH 6/6] automatic tuning applied to some kernel components
Date: Fri, 09 Feb 2007 13:27:38 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Eric W. Biederman wrote:
> Nadia Derbey <> writes:
>>2) why autotuning:
>>There are at least 3 cases where it can be useful
>>. for workloads that are known to need a big amount of a given resource type
>>(say shared memories), but we don't know what the maximum amount needed will be
>>. to solve the case of multiple applications running on a single system, and
>>that need the same tunable to be adjusted to feet their needs
>>. to make a system correctly react to eventual peak loads for a given resource
>>usage, i.e. make it tune up *and down* as needed.
>>In all these cases, the akt framework will enable the kernel to adapt to
>>increasing / decreasing resource consumption:
>>1) avoid allocating "a priori" a big amount of memory that will be used only in
>>extreme cases. This is the effect of doing an "echo <huge_value>
>>2) the system will come back to the default values as soon as the peak load is
> At least the ipc ones are supposed to be DOS limits not behavior
> modifiers.  I do admit from looking at the code that there are some
> consequences of increasing things like shmmni.  However I think we
> would be better off with  better data structures and implementations
> that remove these consequences than this autotuning of
> denial-of-service limits.

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.

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.

Now, talking about DoS limits, akt implements them in a sense: each 
tunable managed by akt has 3 attributes exported to sysfs:
. autotune: enable / disable auto-tuning
. min: min value the tunable can ever reach
. max: max value the tunable can ever reach

Enabling a sysadmin to play with these min and max values makes it 
possible to refine the dynamic adjustment, and avoid that the tunable 
reaches really huge values.


  reply	other threads:[~2007-02-09 12:24 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-16  6:15 [RFC][PATCH 0/6] Automatice kernel tunables (AKT) Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 1/6] Tunable structure and registration routines Nadia.Derbey
2007-01-25  0:32   ` Randy Dunlap
2007-01-25 16:26     ` Nadia Derbey
2007-01-25 16:34       ` Randy Dunlap
2007-01-25 17:01         ` Nadia Derbey
2007-01-16  6:15 ` [RFC][PATCH 2/6] auto_tuning activation Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 3/6] tunables associated kobjects Nadia.Derbey
2007-01-16  6:15 ` [RFC][PATCH 4/6] min and max kobjects Nadia.Derbey
2007-01-24 22:41   ` Randy Dunlap
2007-01-25 16:34     ` Nadia Derbey
2007-01-16  6:15 ` [RFC][PATCH 5/6] per namespace tunables Nadia.Derbey
2007-01-24 22:41   ` Randy Dunlap
2007-01-16  6:15 ` [RFC][PATCH 6/6] automatic tuning applied to some kernel components Nadia.Derbey
2007-01-22 19:56   ` Andrew Morton
2007-01-23 14:40     ` Nadia Derbey
2007-02-07 21:18       ` Eric W. Biederman
2007-02-09 12:27         ` Nadia Derbey [this message]
2007-02-09 18:35           ` Eric W. Biederman
2007-02-13  9:06             ` Nadia Derbey
2007-02-13 10:10               ` Eric W. Biederman
2007-02-15  7:07                 ` Nadia Derbey
2007-02-15  7:49                   ` Eric W. Biederman
2007-02-15  8:25                     ` Nadia Derbey
2007-02-14 13:56 Al Boldi

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