Date: Mon, 25 Jun 2001 16:46:53 -0500 From: Andy Isaacson <adi@hexapodia.org> To: Dag-Erling Smorgrav <des@ofug.org> Cc: John Baldwin <jhb@FreeBSD.org>, cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/i386/i386 machdep.c Message-ID: <20010625164653.B12871@hexapodia.org> In-Reply-To: <xzp7ky0cttj.fsf@flood.ping.uio.no>; from des@ofug.org on Mon, Jun 25, 2001 at 08:12:24PM %2B0200 References: <XFMail.010625121654.jhb@FreeBSD.org> <xzp7ky0cttj.fsf@flood.ping.uio.no>
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On Mon, Jun 25, 2001 at 08:12:24PM +0200, Dag-Erling Smorgrav wrote: > John Baldwin <jhb@FreeBSD.org> writes: > > Err, no. :) The process only sees 4gb of space. Period. The address that > > gets sent to the MMU before the page table lookups (but after the segment > > translation) is 32bits. Not 36, just 32. You can't make a 32-bit address > > acccess more than 4 gig of virtual address space, that's just all there is > > to it. > > I think Andy's point is that the kernel could take advantage of the > additional memory to cache a larger portion of the data set, even if > the app weren't able to access it all at the same time. The app would > do just what it would normally do with such a large dataset, i.e. map > bits of it in and out of its address space (using mmap() and munmap()) > preferably on some sort of LRU basis - business as usual - but the > kernel would be able to keep at least some of what doesn't fit in the > app's address space in memory. Precisely. Interestingly, in my tests on IRIX (the only machine I have access to with enough memory to test these concepts) my test app spends much (27%) of its time in the kernel. Since I was using 512-MB segments, I was probably exceeding the per-node memory on the O2k in question and making the kernel copy pages out of remote memory (or else it was spending all its time handling page table updates); furthermore, on such a machine I should just compile "cc -64" and be done with it. -andy To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe cvs-all" in the body of the message
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