This problem is new to the 2.2.x kernel

When your root disk is a scsi unit you load in inital
ramdisk so you can load the required scsi driver before
mounting the real root file systems.  In the new kernel
the scsi module (aha1542 at least, probably other drivers
too) starts a kernel process named scsi_eh_0  which on
my system gets PID number 8.  This process inherits the open
files from the insmod program which has as current direcotry
the ram disk file system, has the file for the driver open
and the console device.  When the kernel process inherits
these open files, these file will never be closed, so when
the kernel later tries to unmount the ram disk file system
it will fail because of these open files, and because the
file system can't be unmounted the ram area used by this ram
disk file system cannot be freed.  For a normal ram disk
image this is about one and a half megabyts of ram waisted.


The kernel thread si started on the procedure
scsi_error_handler() found in
/usr/src/linux/drivers/scsi/scsi_error.c

This routine has some nice comments about the user space
pages inherited from the insmod process.  The inherited open
files will lock an even bigger number of pages in kernel, in
this case protected file system pages.





Villy