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




hpa@transmeta.com (H. Peter Anvin) said:
> devfs eats lots of kernel memory. That WILL hurt performance.

Care to back your claim with numbers? Do you mean Code Bloat (tm)
or allocated memory for the actual filesystem? The code is ~25k on ia32
(plus some bytes scattered over every devfs aware driver).
For the allocated memory here are my numbers (subject
to my limited understanding of the code):

Every devfs registered device allocates (on ia32):

1 devfs_entry for 46 + strlen(basename-of-device-node) bytes
1 devfs_inode for 46 bytes

Since all device names are fairly short that's ~100 bytes per device.

On my home system (a rather typical workstation, except that it
has SCSI disks, CDROM, and tape) I have (excluding the compatibility
symlinks to old style names) ~350 entries in devfs. Note that
250 of these are for virtual console related devices (64 each of
/def/ttyNN, /dev/vc/NN, /dev/vcc/NN, /dev/vcc/aNN). That means
that even in a system with lotsa hardware (read disks) I wouldn't
expect that number to exceed 500 (+ 2 entries for every pseudo
terminal in use). So we're talking 35kB on my system, 50kB on
large servers, maybe additional 100kB for 1000 ptys in use.


Cheers, Roderich
--
Do not meddle in the affairs of wizards, for they are subtle and quick
to anger. Do not meddle in the affairs of dragons for you are crunchy
and taste good with ketchup. Do not meddle in the affairs of cats, for
they are subtle and will piss on your computer.

Roderich Schupp mailto:rsch@ExperTeam.de
ExperTeam GmbH http://www.experteam.de/
Munich, Germany linux:2.1.115




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