Date: Thu, 2 Aug 2001 08:14:23 -0300 (BRST) From: Rik van Riel <riel@conectiva.com.br> To: Terry Lambert <tlambert2@mindspring.com> Cc: craig <craiglei@pasia.com.cn>, <freebsd-hackers@FreeBSD.ORG> Subject: Re: How to visit physical memory above 4G? Message-ID: <Pine.LNX.4.33L.0108020808560.5582-100000@duckman.distro.conectiva> In-Reply-To: <3B6933F0.FC88449A@mindspring.com>
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On Thu, 2 Aug 2001, Terry Lambert wrote: > Rik van Riel wrote: > > > > Only if you want to use it all within one process. > > > > > > No. It still bites you if you want to do IPC, etc., since you > > > can not guarantee the structures used for this are all within > > > the non-segmented region of memory. > > > > Wrong. Your process can have pages from all over the > > 64 GB mapped into its page tables. > > Try doing this with code pages in one segment, the stack in > another, and the data being referenced in a third. It will > not work. Of course it cannot work. The segments you refer to will map to the linear 4GB space represented by the page tables. Those page tables can map, in their 4GB virtual space, pages from all over the 64GB physical space. > > I've seen a bunch of the machines. They're rather > > popular with the database folks. > > Name an OS that supports this; more than likely, you will > have to appeal to a purpose built embedded system. Linux SCO Unix NT *cough* > > > So it's not unreasonable to think of putting 8G or 16G in > > > a box, and being able to map it all. > > > > You can never map it all, since your virtual address space > > is limited to 4GB... > > Overlays. A technology from the dawn of time, I know, but > so are segment registers. s/You can never map it all/You can never map it all at once/ Happy now? ;) > > Basically the database folks are really keen on keeping > > their 3GB user addressable memory, so the kernel will > > remain limited to 1GB of KVA. > > They shouldn't care, since they are getting more memory. You're telling the people working with 50GB datasets that they shouldn't care about how many of their 512MB segments they can map in at once? ;) > or just wait for IA64, rather than throwing developement > effort into something that will end up in a scrap heap before > it gets reasonable performance, or perhaps before it's even > deployed. Ssssh, don't tell that to the folks who are using such machines today ;) cheers, Rik -- Executive summary of a recent Microsoft press release: "we are concerned about the GNU General Public License (GPL)" http://www.surriel.com/ http://www.conectiva.com/ http://distro.conectiva.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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