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Message-ID: <alpine.LFD.0.9999.0711151403000.4260@woody.linux-foundation.org> Date: Thu, 15 Nov 2007 14:12:14 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Jeremy Fitzhardinge <jeremy@...p.org> cc: William Lee Irwin III <wli@...omorphy.com>, Andi Kleen <ak@...e.de>, Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>, Nick Piggin <nickpiggin@...oo.com.au>, "H. Peter Anvin" <hpa@...or.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: Why preallocate pmd in x86 32-bit PAE? On Thu, 15 Nov 2007, Jeremy Fitzhardinge wrote: > > Once difference is that 64-bit incrementally allocates all levels of the > pagetable, whereas 32-bit PAE preallocates the 4 pmds when it allocates > the pgd. What's the rationale for this? What pitfalls would there be > in making them incrementally allocated? IIRC, the present bit is ignored in the magic 4-entry PGD. All entries have to be present. What earlier CPU's did was to basically load all four values into the CPU when you loaded %cr3. There was no "three-level page table walker" at all: it was still a two-level page table walker, there were just for magic internal page tables that were indexed off the two high bits. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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