Re: DEVFSv50 and /dev/fb? (or /dev/fb/? ???)

Albert D. Cahalan (acahalan@cs.uml.edu)
Fri, 7 Aug 1998 18:18:54 -0400 (EDT)


Terry L Ridder writes:
> To quote H. Peter Arvin again:
>
> <Begin Quote>
> Counter question: how much kernel memory does it take to
> keep a million devices with all their info (atime, mtime,
> ctime, permissions, ownership all included!)
> <End Quote>
>
> Note no one from the dev_fs side has answered this question yet.

I assume he realized how dumb that was after he posted it, and he
was unable to cancel it. You took it seriously?

Think about it for two seconds. The devfs generates devices as needed.
If you have a static /dev on a normal filesystem, you have to have
all 8 million possible SCSI devices. With devfs, you don't.

(The scsidev tool is a hack every bit as flawed as devfs, with few
of the good points that devfs has. You can't make be believe that
you really want to run scsidev every time you boot, and it only
handles SCSI anyway.)

> dev_fs uses too much of kernel memory and by doing so inflicts a
> performance hit.

You are making fiction now.

It uses a few pages. That would be maybe 0.1% of memory, dropping
as the years go by. (it is a fixed cost, which is nothing against
exponential memory growth)

The normal /dev eats memory too. It requires inodes and dcache entries.

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