Date: Wed, 24 Apr 2002 16:38:08 -0700 From: Terry Lambert <tlambert2@mindspring.com> To: Steve O'Hara-Smith <steve@sohara.org> Cc: scrappy@hub.org, freebsd-current@freebsd.org, freebsd-stable@freebsd.org Subject: Re: FreeBSD 4.5-STABLE not easily scalable to large servers ... ? Message-ID: <3CC741E0.2BB79E0C@mindspring.com> References: <20020422091602.O1721-100000@mail1.hub.org> <3CC40A62.B40E816F@mindspring.com> <20020424191849.3a81b126.steve@sohara.org>
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Steve O'Hara-Smith wrote: > On Mon, 22 Apr 2002 06:04:34 -0700 > Terry Lambert <tlambert2@mindspring.com> wrote: > > TL> FreeBSD doesn't currently support bank selection. Peter was > TL> working on it, last time I heard. Linux supports it, at an > TL> incredible performance penalty. > > This inspired an off the wall thought that may be insane. Would > it be possible (on a >4Gb system) to address 4Gb of RAM and write a driver > to make the rest appear as a device, which could then be used for a > preferred or (even neater) first level swap. Only if you reserved a window for it. Say 1G of KVA, though last I checked the bank selection granularity wasn't fine enough for that. Memory in the window can *never* be a target for DMA, and should *probably* never be used for kernel structures. If you ever programmed graphics on a TI 99/4A, which has a 4k visible window onto screen memory, or programmed code on the Commodore C64 to use the 32K of RAM-under-ROM, or programmed in DOS or CP/M using Overlays, then you'll be familiar with the problem. -- Terry To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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