Date: Sat, 19 Feb 2000 12:10:14 +1100 From: Patryk Zadarnowski <patrykz@ilion.eu.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: Arun Sharma <adsharma@sharmas.dhs.org>, freebsd-hackers@FreeBSD.ORG Subject: Re: 64bit OS? Message-ID: <200002190110.MAA31421@mycenae.ilion.eu.org> In-Reply-To: Your message of "Fri, 18 Feb 2000 16:06:55 -0800." <200002190006.QAA82061@apollo.backplane.com>
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> :... > :and Linux essentially treats hardware page tables as TLBs. > : > :The problem with the above approach is duplication of information between > :Linux page tables and hardware page tables and inefficient use of memory > :for page tables. > : > :I think OSes like FreeBSD which don't have a concept of machine independent > :page table are essentially free to do anything in the hat layer and thus > :have more flexibility. > > If I understand the hardware hash table method correctly, then > I think the absolute best choice for FreeBSD is to use that method > as it will allow us to get rid of the scaleability problems we have > with the pv_entry_t scheme we use for IA32. The number of pv_entry_t's > in an IA64 architecture wind up being fixed. How big can we make the > hardware-assisted hash table? > > Also, a hash table scheme is a much better fit for a 64 bit address > space model, especially with sparse mappings. The MIPS R4K and later > all use a hash table scheme and it seems to work well for them. Kevin Elphinstone did a PhD thesis on TLB structures for 64 bit address spaces and it turns out that hash tables perform quite poorly. I'd suggest GPTs instead, or maybe LPCtrie that Chris Szmajda has been working on here at UNSW. Both have the advantage of supporting multiple page sizes that IA64 (and Alpha) offer, and hence dramatically increasing the TLB coverage over what Linux (or any other commercial OS that took a bite at IA64) can achieve. Kevin's paper's at: ftp://ftp.cse.unsw.edu.au/pub/users/disy/papers/Elphinstone:phd.ps.gz Maybe that way we can somehow make use of the Itanium's 4GB page size ;)))) Pat. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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