updatedb

Rene Herman
2007-07-26T03:59:53Z

On 07/25/2007 07:15 PM, Robert Deaton wrote:

> On 7/25/07, Rene Herman <rene.herman@gmail.com> wrote:

>> And there we go again -- off into blabber-land. Why does swap-prefetch
>> help updatedb? Or doesn't it? And if it doesn't, why should anyone
>> trust anything else someone who said it does says?

> I don't think anyone has ever argued that swap-prefetch directly helps
> the performance of updatedb in any way

People have argued (claimed, rather) that swap-prefetch helps their system
after updatedb has run -- you are doing so now.

> however, I do recall people mentioning that updatedb, being a ram
> intensive task, will often cause things to be swapped out while it runs
> on say a nightly cronjob.

Problem spot no. 1.

RAM intensive? If I run updatedb here, it never grows itself beyond 2M. Yes,
two. I'm certainly willing to accept that me and my systems are possibly not
the reference but assuming I'm _very_ special hasn't done much for me either
in the past.

The thing updatedb does do, or at least has the potential to do, is fill
memory with cached inodes/dentries but Linux does not swap to make room for
caches. So why will updatedb "often cause things to be swapped out"?

[ snip ]

> Swap prefetch, on the other hand, would have kicked in shortly after
> updatedb finished, leaving the applications in swap for a speedy
> recovery when the person comes back to their computer.

Problem spot no. 2.

If updatedb filled all of RAM with inodes/dentries, that RAM is now used
(ie, not free) and swap-prefetch wouldn't have anywhere to prefetch into so
would _not_ have kicked in.

So what's happening? If you sit down with a copy op "top" in one terminal
and updatedb in another, what does it show?

Rene.