The magical missing 6 megabytes of mysterious RAM

agent dero dero at
Tue May 6 12:23:26 PDT 2003

I don't beleive it can be BIOS sharing the system RAM with other devices,
because my box that is in question has a 1MB Graphic card, and sits in the
corner. Absolutely no work is done on the box physically. And I think the
1MB graphic card is enough to display BIOS and show the kernel and OS
booting. (even if no monitor is attached)

I am almost confident that is the kernel loaded into memory. I haven't
seen much of a difference in real and availible memory between a custom
kernel, and GENERIC. But, before the messages in /var/log/ are createde
the FreeBSD boot manager must boot, and then it starts loading the kernel.
So I am 99% sure it is the kernel being loaded into the active RAM.
I will be able to test this more if I get a box with less RAM, that needs
a good compiled kernel.  But I think the issue should be put to rest with,
the 6 "missing megabytes" being the kernel. (which must always be in the
physical RAM)

> Yes and no.  You can't reuse any memory used for page tables,
> so that's "pure overhead".  You also can't reuse any memory
> that has not been marked as swappable.  If you allocate memory
> in the kernel, it will be permanently subtracted from the "avail"
> (it just doesn't give you another message to the effect of any
> chanes in "avail", because it would be printf'ing to the console
> all the time, if it did), since kernel memory is allocated as
> being type-stable.
--schnip to other message--
> I think you missed my point - I wasn't saying that FreeBSD is hiding
> anything, nor was I talking about the "missing 6mb problem" directly.
> You pretty much repeated my point though - "Since the BIOS is where
> FreeBSD obtains the "real memory" number" - which is what I said, that
> the BIOS takes the physical RAM, subtracts what it needs for devices
> like video cards (that "borrow" from physical main memory), then reports
> that result to any OS/Apps/etc that ask for it.  That is why my system
> doesn't show the 256Mb of memory it has in it, it shows something like
> 224Mb (32Mb is set aside for the video card)..
> Unless I am totally missing your point this morning.. :)

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