Quotes of the week [LWN.net]

It's really very simple: overcommit off you must have enough RAM and swap to hold all allocations requested. Overcommit on - you don't need this but if you do use more than is available on the system something has to go.

It's kind of like banking overcommit off is proper banking, overcommit on is modern western banking.

-- Alan Cox

Consider the fact that i get 1000 times more bugreports aided by strace, which has 1000 times more overhead than even the slowest of uprobes approaches.

This simple fact tell us that while performance matters, it is of little use if good utility and a clean design is not there. (in fact sane and clean design will almost automatically result in good performance too down the line, but i digress.) Faster crap is still crap.

-- Ingo Molnar

Forks aren't always great, but I honestly don't think of forks as being a bad thing and I've tried to instill in Google the same ethic.

In fact, I'd say that the various forks of Linux, and how the Linux maintainers have roped back in some forks (and let others go on their merry way) is what made the Linux kernel great and not just a BSD rehash.

-- Chris DiBona

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Quotes of the week

Posted Feb 5, 2010 21:56 UTC (Fri) by leoc (subscriber, #39773) [Link]

Not all western banks "overcommit" money, just the ones people pay attention to.

Banking analogy of Linux memory management

Posted Feb 5, 2010 22:13 UTC (Fri) by giraffedata (subscriber, #1954) [Link]

Is there any bank in the world that operates with overcommit off (i.e. holds a dollar in cash for every dollar on deposit)? I wouldn't call that "proper" banking, just a different, obsolete kind of banking. I believe a long time ago, there were banks that functioned just as a safe storage place and conduit for money, and depositors paid for the service, but there doesn't seem to be any interest in that now.

Banking analogy of Linux memory management

Posted Feb 6, 2010 3:59 UTC (Sat) by bronson (subscriber, #4806) [Link]

Agreed, a capitalization ratio of 50% would be insane. Even the ancient Greeks didn't require that.

Cap ratio only deals with how money moves from place to place so it's more like the virtual memory / buffer management system. Overcommit talks about exactly what is BACKING the memory or currency.

Basically:
Overcommit Off is the gold standard.
Overcommit On is fractional reserve lending.

200 years ago, to print a $1 bill, a government first need to find $1 worth of gold to back it. No gold, no money. This is safe but glacially slow -- you can only grow your economy as fast as you can mine gold.

In 1933, the United States moved to fiat money where nothing at all backs the currency -- nothing except the faith that one can redeem it for physical value (i.e. goods and services) in the future.

Pretty similar to overcommit, where nothing backs a memory allocation -- nothing except for the faith that it can be redeemed for physical memory in the future. Call it fiat memory.

And that's about as deep as the analogy goes, best not to look too close. :)

Banking analogy of Linux memory management

Posted Feb 6, 2010 4:24 UTC (Sat) by giraffedata (subscriber, #1954) [Link]

Thanks for the banking background.

However, I don't think we're talking about capitalization ratio, which has to do with how much a business borrows to fund its operation (its leverage), but rather the reserve ratio, which is how much cash a bank keeps on hand to pay back depositors who wish to withdraw their demand deposits.

Overcommit off is a 100% reserve ratio.

Wikipedia says the legal minimum reserve ratio in the US is 10%. I heard it was once 3%.

Reserve ratios

Posted Feb 7, 2010 22:02 UTC (Sun) by man_ls (subscriber, #15091) [Link]

You are probably right. Note that if banks were required to have 100% reserve ratios then they would not be able to invest the money that people deposit there, not even to lend this money to other people. So essentially the money would be frozen and would generate no wealth at all. What Cox calls "proper banking" would be a disaster.

Also note that money deposited in a bank has a non-linear behavior that memory does not have. The Wikipedia article shows why: lent money can be deposited again, and then lent again, and so on.

As others have pointed out, maybe Cox naïvely refers to the gold standard, not noticing that the price of gold is an arbitrary measure, as artificial as any other. Nowadays money creates itself and is properly accepted by all as the imaginary magnitude it really is.

Banking analogy of Linux memory management

Posted Feb 6, 2010 15:13 UTC (Sat) by nix (subscriber, #2304) [Link]

This is safe but glacially slow

Ask the Spanish about that sometime.

What it really means is that your money supply is out of the hands of politicians. That's a good thing, in a sense, but the downside is that if someone makes a big gold discovery (e.g. Spain) you suffer massive inflation; if your economy needs to grow, it can't; and if your economy suddenly *shrinks* the gold standard will throttle it and stop it recovering. The Great Depression is of course the canonical example of this.

The gold standard works great when things are going well, but if there's a sudden shock it's a disaster, and it can be the source of sudden shocks. In this it is very similar to every other scheme for backing money yet discovered.

Banking analogy of Linux memory management

Posted Feb 7, 2010 0:41 UTC (Sun) by pflugstad (subscriber, #224) [Link]

Our current problems are that the US banking industry was deregulated (back in the mid 80's) and allowed to basically start gambling with EVERYONE's money, taking ridiculous bets and doing other absolutely insane things. There were alternatives:

http://www.nytimes.com/2010/02/01/opinion/01krugman.html