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On preload



Hi all,

Ok, I read the preload thread.  Most of the questions asked are answered
here:

  http://behdad.org/preload.pdf

Chapters 6, 7, and 8 is what one needs to read.

Random comments:

  - Yes, slows down boot.  Can be "improved" by making preload less
aggressive.  In fact there are different knobs to allow setting
aggressiveness at boot time and after separately.  All documented in the
config file and the above document.

  - Much of the slow down couldn't be avoided back in the day, but in
the next version I'm using ionice to start preload.  That should improve
things.

  - One major thing that I'm not happy about in preload is that it
doesn't readahead directories, nor does it readahead stat calls.  And
that's where the best bang for the memory is.  Read Chapter 7.  That's
the advantage of SuSE preload over Fedora preload and Fedora readahead.
SuSE preload uses a static list of course.

There was a Google Summer of Code student working for Ubuntu this past
summer trying to fix these and implement block reordering.  Obviously
that needs kernel patches.  No idea where it got.

  - There's one place that no one can argue preloading is bad: after
login screen is shown and before password entry is completed.  GDM has a
setting to hookup a prefetcher into it.  It's worthwhile making preload
be started then and shutdown for example 10 minutes after login.  With
some tricks and dances, one can make it do really awesome things in that
idle period.

  - So far preload has been idling in kind of unmaintained state, though
after Marc's interest in putting in Fedora I've now merged all the
patches I received (ionice, merging requests, sorting based on block
location, parallel fetching) and will make a new release sometime
soonish.  Note that also due to a silly bug, the current version doesn't
sort request AT ALL.  It's supposed to sort based on file name, but the
compare function has a typo making it a noop.


Anyway, people should read at least Chapter 7 and 8 of the PDF before
discussing further.  I'll try to get that release out in the mean time
so measurements can be more meaningful.

Cheers,

behdad


On Wed, 2008-01-23 at 23:42 +0900, Marc Wiriadisastra wrote:
> Hey mate,
> 
> Quick question do you have any data on benchmarks. Some people are
> considering putting preload as a default application in Fedora. I agree
> with them but I'm trying to benchmark some stuff and it's pretty hard to
> actually get numbers.
> 
> The other question which came from Rahul is " did you talk to behdad
> about what improvements can be made to show some stats for example?"
> Also any potential improvements in the next version?
> 
> Cheers,
> 
> Marc 
> On Sun, 2008-01-20 at 22:44 -0500, Behdad Esfahbod wrote:
> > Thanks Marc.  I unsubscribed from devel list and a slew of other ones a
> > while ago when I figured that I'm not reading them anyway.
> > 
> > Would be interesting to see what more people think of it.  I have more
> > of a reason to get that release out now :).
> > 
> > Cheers,
> > 
> > behdad
> > 
> > On Sun, 2008-01-20 at 23:12 +0900, Marc Wiriadisastra wrote:
> > > Hey Behdad,
> > > 
> > > Not sure if you follow the devel list to much since I don't see you
> > > posting to much.
> > > 
> > > A preliminary review of preload from Linus.
> > > 
> > > https://www.redhat.com/archives/fedora-devel-list/2008-January/msg01948.html
> > > 
> > > Cheers,
> > > 
> > > Marc
-- 
behdad
http://behdad.org/

"Those who would give up Essential Liberty to purchase a little
 Temporary Safety, deserve neither Liberty nor Safety."
        -- Benjamin Franklin, 1759


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