Re: fastboot, diskstat

[Avi Kivity <avi@argo.co.il>]

Andrew Morton wrote:

>The above data is enough for performing a crude preload:
>
>a) Boot the machine
>
>b) Boost the disk queue size, set the VFS readahead to zero, open
>   /dev/hda1 and all the regular files, hose reads at the disk via
>   fadvise().  Restore VFS readahead and queue size, continue with boot.
>  
>
opening all these files will require synchronous reads of their 
directories and inodes, so you might need to split b) into first opening 
and reading /dev/hda1, then opening and reading the regular files.

>And I suspect that the whole thing will be of marginal benefit.  Although
>things might be better now that files are laid out with the Orlov allocator
>(make sure that the distro was installed with a 2.6 kernel!  The file
>layout will be quite different if the installer used a 2.4 ext3).
>
>Of course the next step is to rewrite files so that they are more
>favourably laid out on disk.  Tricky.  Or dump all pagecache to some temp
>file in a nice linear slurp and preload that, copying it all to the
>appropriate per-inode pagecaches and taking care of files which have been
>modified.  Trickier ;)
>  
>
another possibility: use a device mapper module under /dev/hda1 that 
records I/O patterns, then relocates blocks to fit that pattern, so that 
the normal boot sequence ends up issuing sequential disk writes.

parallelized initscripts will probably defeat this, though.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.