Date: Wed, 13 Aug 2008 08:48:26 -0500 From: Nathan Whitehorn <nwhitehorn@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-arch@freebsd.org Subject: Re: UMA MD Small Allocator Runtime Switching Message-ID: <48A2E62A.9060604@freebsd.org> In-Reply-To: <200808051024.27043.jhb@freebsd.org> References: <48981C19.8060009@freebsd.org> <200808051024.27043.jhb@freebsd.org>
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John Baldwin wrote: > On Tuesday 05 August 2008 05:23:37 am Nathan Whitehorn wrote: >> I'm working on the PowerPC G5 port right now, and have run into a >> problem with the way the UMA small allocator works. On G3/G4 systems, >> there is a direct physical->virtual mapping, and on G5s there isn't. All >> of the infrastructure is in place to support both types of system with a >> single kernel image, except that UMA_MD_SMALL_ALLOC must be switched >> on/off at runtime. >> >> One solution is to put if (direct_map) use_nonsmall_case() into the MD >> small_alloc/free() routines and define UMA_MD_SMALL_ALLOC everywhere. >> This works well, except that the MI UMA code then sets booted = 1 too >> early in the boot process, before the kmem_alloc*() routines are available. >> >> Basically, I need to find a way have an MD UMA allocator without the MI >> UMA code assuming anything about how it works internally. Maybe adding a >> UMA_MD_ALLOC_LATE define to prevent setting booted=1 early on? >> -Nathan > > Have you considered creating an artificial direct map region in the address > space on the G5? Some of the other 64-bit ports (amd64 and sparc64) do this > to gain the benefits of the direct map even though it isn't a mandated part > of the architecture like it is on some other platforms (alpha and mips). I thought about it, but we can only use 4K pages on the G5 so this would put a large amount of pressure on the page table. IBM removed the block translation mechanism from the G5 and the CPU's superpage support is not available in the 32-bit compatibility mode under which we currently run. -Nathan
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