Messages in this thread | | | Date | Wed, 23 Jan 2002 10:43:23 +0100 | From | Martin Knoblauch <> | Subject | Re: Possible Idea with filesystem buffering. |
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> Re: Possible Idea with filesystem buffering. > > From: Richard B. Johnson (root@chaos.analogic.com) > Date: Tue Jan 22 2002 - 17:10:27 EST > > > We need a free-RAM target, possibly based upon a percentage of > available RAM. The lack of such a target is what causes the > out-of-RAM condition we have been experiencing. Somebody thought > that "free RAM is wasted RAM" and the VM has been based upon > that theory. That theory has been proven incorrect. You need
Now, I think the theory itself is OK. The problem is that the stuff in buffer/caches is to sticky. It does not go away when "more important" uses for memory come up. Or at least it does not go away fast enough.
> free RAM, just like you need "excess horsepower" to make > automobiles drivable. That free RAM is the needed "rubber-band" > to absorb the dynamics of real-world systems. >
Correct. The free target would help to avoid the panic/frenzy that breaks out when we run out of free memory.
Question: what about just setting a maximum limit to the cache/buffer size. Either absolute, or as a fraction of total available memory? Sure, it maybe a waste of memory in most situations, but sometimes the administrator/user of a system simply "knows better" than the FVM (F == Fine ? :-)
While being there, one could also add a "guaranteed minimum" limit for the cache/buffer size. This way preventing a complete meltdown of IO performance. True64 has such limits. They are usually at 100% (max) and I think 20% (min), giving the cache access to all memory. But there were situations where a max of 10% was just the rigth thing to do.
I know, the tuning-knob approach is frowned upon. But sometimes there are workloads where even the best VM may not know how to react correctly.
Martin -- ------------------------------------------------------------------ Martin Knoblauch | email: Martin.Knoblauch@TeraPort.de TeraPort GmbH | Phone: +49-89-510857-309 C+ITS | Fax: +49-89-510857-111 http://www.teraport.de | Mobile: +49-170-4904759 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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