Messages in this thread |  | | Date | Thu, 26 Oct 2000 13:34:00 -0500 (CDT) | From | Jesse Pollard <> | Subject | Re: Topic for discussion: OS Design |
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Andi Kleen <ak@suse.de>: > On Thu, Oct 26, 2000 at 11:00:03AM -0500, Jesse Pollard wrote: > > Keith Owens <kaos@ocs.com.au>: > > > > > > On Thu, 26 Oct 2000 09:17:49 -0400 (EDT), > > > "Richard B. Johnson" <root@chaos.analogic.com> wrote: > > [snip] > > > >This shows that out of 34,678 bytes we needed, we wasted 6282, ~1.5 > > > >pages. Since there are 5 modules, we waste about 1/3 page per module. > > > > > > > >So I don't, as you say; "... waste 1/2 page or more per module". > > > > > > Statistics say that the average loss will be 1/2 page per module. Some > > > will waste more, some will waste less, average is 1/2 the unit. > > > > Only if the size of a random module can be between 0 and a full page.... > > > > Module sizes are skewed data... there is a minimum size for a module > > (somewhere around 1k, I believe - didn't measure it), and if the module > > is going to DO anything then it will be between 1-2K. This skews the data > > sample such that you are only loosing 1/2 of (1 page - minimum) or 1/2 of > > 3K = 1.5K. Hence the 1/3 measured loss will be closer to the correct > > theoretical loss than 1/2. > > You're forgetting that longer modules wrap at the end to a full page, which > makes all values possible again.
You appear to be right.... I thought of them as anomalies, but there are more of them than I believed. I was also thinking of the total number of pages for the modules rather than the total number of modules.
The following is from my server (SCSI based, but does have IDE disks too):
module size pages loss --------- ------ -------- -------- vfat 9116 0 (unused) 2.22559 0.774414 smbfs 26232 0 (unused) 6.4043 0.595703 msdos 5180 0 (unused) 1.26465 0.735352 isofs 17432 0 (unused) 4.25586 0.744141 fat 30240 0 [vfat msdos] 7.38281 0.617188 3c509 6004 1 1.46582 0.53418 ide-probe 6244 0 1.52441 0.475586 ide-disk 5800 0 1.41602 0.583984 ide-cd 23028 0 5.62207 0.37793 ide-mod 44536 0 [ide-probe ide-disk ide-cd] 10.873 0.126953 sb 33876 0 8.27051 0.729492 uart401 5968 0 [sb] 1.45703 0.542969 sound 57336 0 [sb uart401] 13.998 0.00195312 soundlow 224 0 [sound] 0.0546875 0.945312 soundcore 2308 5 [sb sound] 0.563477 0.436523 serial 19284 0 (unused) 4.70801 0.291992 lp 5180 0 1.26465 0.735352 parport_pc 5652 1 1.37988 0.620117 parport 7208 1 [lp parport_pc] 1.75977 0.240234
averages: 3.99423 0.532072
So the average size of a module is 3.9 pages and the average size of lost space in a page IS close to .5 (actually a little greater).
If the two anomilies (ide-mod and sound) are dropped then the average size of lost space is 0.525288, even close to .5.
The only remaining anomily is the soundlow module (size 224). If this one is dropped too then the average size of lost page space is 0.475535.
Looking at this, the overall wasted space is a whopping 10.1 pages or 40K. Not bad at all.
BTW, all values taken from a Linux 2.2.13.SMP system.
------------------------------------------------------------------------- Jesse I Pollard, II Email: pollard@navo.hpc.mil
Any opinions expressed are solely my own. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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