readahead - from a tar file

[Shawn Rutledge]

On 10/23/07, Mildred <ml.mildred593 at online.fr> wrote:
> Le Mon 22/10/2007 à 14:20 Shawn Rutledge à écrit:
> > It would probably be enough to have a different selection in the boot
> > loader, like the one for "profile", which does not use the tarball at
> > all (and regenerates the tarball later).
>
> Or it could be enough to tell all those who want to change the
> configuration while the system is down, to write directly in the tar
> file. Since the tar file format is well-known this does not have the
> drawback of the binary file format presented on the other thread
> (Caching jobs).

They are nearly independent ideas, and I suspect both would help.  But
putting files to be read-ahead into a tar file could be used with any
variety of init, not just upstart.

The inspiration is how fast it can be to restore a system from
hibernation.  What tricks do they use for that?  One is that it's just
one big block on the disk, being read directly into memory.  And of
course also, no initialization of processes is being done, because
they were already running when the hibernation occurred.  If we can
make regular booting more like the un-hibernation process it would be
much faster.  Unfortunately because code in general has bugs and
underdeveloped features and is always in flux, we've never gotten to
the ideal case which would be to have a static "boot image" that can
just be plopped into memory and all the known processes resumed from
their known state in the image, without any "clean booting"
initialization stuff.  (But emacs is started that way, isn't it?)
Just doing the readahead faster is an incremental step, not really
very radical.

> I think it could be a good idea to increase the boot speed. Even if I
> don't know if it is worthwhile.