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Message-ID: <474346DE.5050305@zytor.com> Date: Tue, 20 Nov 2007 12:43:10 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: Andi Kleen <ak@...e.de> CC: Christoph Lameter <clameter@....com>, akpm@...ux-foundation.org, travis@....com, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, linux-kernel@...r.kernel.org Subject: Re: [rfc 08/45] cpu alloc: x86 support Andi Kleen wrote: > On Tuesday 20 November 2007 04:50, Christoph Lameter wrote: >> On Tue, 20 Nov 2007, Andi Kleen wrote: >>> I might be pointing out the obvious, but on x86-64 there is definitely >>> not 256TB of VM available for this. >> Well maybe in the future. > > That would either require more than 4 levels or larger pages > in page tables. > >> One of the issues that I ran into is that I had to place the cpu area >> in between to make the offsets link right. > > Above -2GB, otherwise you cannot address them > This limitation shouldn't apply to the percpu area, since gs_base can be pointed anywhere in the address space -- in effect we're always indirect. Obviously the offsets *within* the percpu area has to be in range (±2 GB per cpu for absolute offsets, slightly smaller for %rip-based addressing -- obviously judicious use of an offset for gs_base is essential in the latter case). Thus you want the percpu areas below -2 GB where they don't interfere with modules or any other precious address space. -hpa - 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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