Date: Thu, 2 Aug 2001 11:28:13 -0300 (BRST) From: Rik van Riel <riel@conectiva.com.br> To: mark tinguely <tinguely@web.cs.ndsu.nodak.edu> Cc: <culverk@wam.umd.edu>, <craiglei@pasia.com.cn>, <freebsd-hackers@FreeBSD.ORG>, <tlambert2@mindspring.com> Subject: Re: How to visit physical memory above 4G? Message-ID: <Pine.LNX.4.33L.0108021115500.5582-100000@duckman.distro.conectiva> In-Reply-To: <200108021414.f72EEBS78044@web.cs.ndsu.nodak.edu>
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On Thu, 2 Aug 2001, mark tinguely wrote: > The addressing use 64 bits for a memory pointer and the additional > page indirection add to the overhead. The stickler is the MMU is > still 32 bits. This means the PAE must segment the 64GB space into > 4GB segments or 4 1GB segments. The OS must manage which pages are > viewable to the process at this time. There's a better option. The application does this stuff itself, by mapping and unmapping SHM segments. This needs to be done anyway, since the application wouldn't be happy if the OS randomly remapped its address space to different pages ;)) > There is a third mode of addressing using 2MB pages (simular to the > 4MB page addressing mode for the 32 bit addressing scheme) that will > only give a process access to 4GB of memory (not segmentable to > a larger space, but can address physical memory located above the 4GB > address). You can do that with 4kB pages too. Both the middle page directory and page table have 512 64-bit entries, so you can simply map 4kB pages from above the 4GB physical boundary... regards, 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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