linux-kernel - Does a kernel assisted file system reorder make sense?

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Date:	Sun, 15 Nov 2009 11:39:56 +0100
From:	Christian Volkmann <haveaniceday@...sv.de>
To:	linux-kernel@...r.kernel.org
Subject: Does a kernel assisted file system reorder make sense?

Hi,

I just have read some articles about faster booting systems
(Ubuntu 9.10) , SSD, hard disks, latency and seek times...

Due to this I have some ideas which I like to discuss.
I am for sure not the first with this idea, but I do not
find any discussion about it. :)

Shouldn't it be possible for the kernel to provide an ordered
loaded block list read from disk ? This could be used for a kind
of "forced reorder" for a file system tool.

May be this would also fasten the system start from a hard disk.
I could imagine a scenario like:
- kernel start (boot loader )
- kernel to keep a list of the read blocks (on a per filesystem base)
- kernel to log this list just before init starts.
- on demand: kernel to continue the recording
- on demand: kernel can signaled to log this list.
   (e.g. graphic log in ready )

This logged list could be use from a new tool like "e2reorder"
for ext2/3/4 to reorder the blocks within the file system(s) to
reduce the seek delay for a start from a hard disk.

The logged list could also be used as a "to load/cache first" list
for the kernel/initrd boot. This might fasten the start without
special file system tools or for file systems without support.

But this would only make sense if a system boot is delayed by
hard disk seek times. I have no SSD to check if a SSD boots
faster. Does anyone have the experience if a SSD boots faster?

Best regards,

Christian

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