On Fri, Mar 04, 2011 at 07:48:55PM +0200, Andriy Gapon wrote: > on 04/03/2011 16:36 Dmitry Krivenok said the following: > > Hello Hackers, > > I've limited the amount of physical memory visible for my FreeBSD-8.2 by > > adding > > the following in loader.conf: > > > > $ cat /boot/loader.conf | grep hw.physmem > > hw.physmem="500M" > > $ > > > > However, according to sysctl, the system sees > > > > $ sysctl hw.physmem > > hw.physmem: 507445248 > > $ > > > > The difference is (500 * 2**20 - 507445248) / 2**20 == 16.0625 Mb. > > How does the system use this "hidden" memory? > > Some memory is taken by structures that describe usable pages. > There is one vm_page_t structure per each 4KB page. > I believe that that memory is excluded from physmem.
hw.physmen doesn't set the physucal memory - it sets the maximum physical address. But there are unuseable addresses used for IO - e.g. the 640k-1M range and board depended PCI io-ranges. I set hw.physmem="8704M" on my 8G system to reduce memory (last bytes are declared uncacheable by broken BIOS). -- B.Walter <be...@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm. _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "freebsd-hackers-unsubscr...@freebsd.org"
