readahead changes

[Scott James Remnant]

On Thu, 2006-09-21 at 09:31 +0000, robepisc wrote:

> 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!

> 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?
> 
It has more than that, but there's no reduction in startup time by
booting with mem=256M -- as has previously been discussed on this
mailing list.

> If you have less than a certain amount of RAM, readahead might _slow down_ the
> LiveCD startup.  This is (IMHO) what Mike meant.
> 
readahead isn't used on the LiveCD because it upsets unionfs/squashfs.

Scott
-- 
Scott James Remnant
scott at ubuntu.com
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