Messages in this thread | | | Date | Sat, 24 Jan 2004 15:35:51 -0800 | From | Andrew Morton <> | Subject | Re: Request: I/O request recording |
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Felix von Leitner <felix-kernel@fefe.de> wrote: > > I would like to have a user space program that I could run while I cold > start KDE. The program would then record which I/O pages were read in > which order. The output of that program could then be used to pre-cache > all those pages, but in an order that reduces disk head movement. > Demand Loading unfortunately produces lots of random page I/O scattered > all over the disk.
I wrote a similar thing in September of 2001. What you do is:
- Reboot the system, wait until everything is steady-state (eg: X has started, applications are loaded).
- Load a kernel module which dumps the current contents of the pagecache (filename/offset-into-file) into a file.
(The kernel module writes to modprobe's stdout, so you just do
modprobe fboot-dump > /tmp/fboot-dump.out
I'm very proud of this.)
- Post-process the resulting output into a database which is used on the next reboot.
- reboot
- This time a userspace application cuts in real early and reads the database and preloads all the pagecache using "optimal" I/O patterns so that everything which you will need in the subsequent boot is already in memory.
So it's all an attempt to optimise the boot-time I/O patterns. It was pretty much a waste of time, gaining only 10% or so, from memory. You could get just as much or more speedup from simply launching all the initscripts in parallel, although this did tend to break stuff.
Anyway, the code's ancient but might provide some ideas:
http://www.zip.com.au/~akpm/linux/fboot.tar.gz
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