readahead changes

[robepisc]

Scott James Remnant <scott <at> ubuntu.com> writes:

> 
> On Wed, 2006-09-20 at 08:09 -0700, Mike Bird wrote:
> > On Tuesday 19 September 2006 21:33, Scott James Remnant wrote:
> > >  - the machine was my laptop, a fairly typical P-M which had been
> > >    installed with dapper and upgraded through edgy
> > 
> > With low RAM, readahead may increase startup time as blocks are read
> > by readahead, expired from the cache, then read by the normal startup
> > process.
> > 
> The amount of memory used by the default readahead lists is 61.5MB.
> 
> > What, if any, are these RAM thesholds for the most common Ubuntu
> > configurations?
> > 
> The recommended RAM for edgy (using the "$500 PC from Dell in April"
> metric) is 256MB.
> 
> Given the readahead size of 61.5MB, and the average kernel usage of 18M,
> that gives us a not unreasonable minimum of 80MB or so for Ubuntu.
> 
> This is obviously too high for machines with 64MB of memory or less, but
> those I suspect would be using a different derivative which need not
> ship readhead (or start so much!).
> 
> Also once you've got that little memory, I suspect you won't mind so
> much if the boot process takes a few seconds more, or even notice!
> 
> Scott

Ok, but how much RAM does your laptop (the one you used for your tests) have?
If more than 256M, have you tried with mem=256M as a kernel boot parameter?
Would you still notice a reduction in startup time?
If you have less than a certain amount of RAM, readahead might _slow down_ the
LiveCD startup.  This is (IMHO) what Mike meant.

BTW, thanks for your efforts to speedup Ubuntu!

Ciao,
  robepisc