Date: Mon, 20 Sep 2004 13:55:22 -0400 From: John Baldwin <jhb@FreeBSD.org> To: "Poul-Henning Kamp" <phk@phk.freebsd.dk> Cc: cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/boot/i386/boot2 boot2.c Message-ID: <200409201355.23134.jhb@FreeBSD.org> In-Reply-To: <15147.1095545330@critter.freebsd.dk> References: <15147.1095545330@critter.freebsd.dk>
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On Saturday 18 September 2004 06:08 pm, Poul-Henning Kamp wrote: > In message <200409181659.48310.jhb@FreeBSD.org>, John Baldwin writes: > >On Saturday 18 September 2004 03:08 am, Poul-Henning Kamp wrote: > >> In message <200409180207.i8I27044010045@repoman.freebsd.org>, John > >> Baldwin writ > >> > >> es: > >> >jhb 2004-09-18 02:07:00 UTC > >> > > >> > FreeBSD src repository > >> > > >> > Modified files: > >> > sys/boot/i386/boot2 boot2.c > >> > Log: > >> > A long, long time ago in a CVS branch far away (specifically, HEAD > >> > prior to 4.0 and RELENG_3), the BTX mini-kernel used paging rather > >> > than flat mode and clients were limited to a virtual address space of > >> > 16 megabytes. Because of this limitation, boot2 silently masked all > >> > physical addresses in any binaries it loaded so that they were always > >> > loaded into the first 16 Meg. Since BTX no longer has this limitation > >> > (and hasn't for a long time), remove the masking from boot2. This > >> > allows boot2 to load kernels larger than about 12 to 14 meg (12 for > >> > non-PAE, 14 for PAE). > >> > >> Does this also give us better space for isa_dma bounce buffers ? > > > >Err, I don't see how it could. This only affects how boot2 handles > > addresses in the executables it loads, it doesn't affect how the kernel > > manages memory at all. > > it was the "so that they were always loaded into the first 16 Meg" that > triggered a neuron here. > > We're seeing isa-dma bounce buffers getting hard to get hold of these > days. Humm, we've always loaded the kernel as low as possible, at least in the 3.x+ era. 3.x loaded it at 1MB IIRC, and with Bosko's changes to avoid the Intel PSE bug we switched to 4MB for non-PAE and 2MB for PAE (to avoid mapping the PSE page starting with physaddr of 0). Also, the kernel is linked such that KERNBASE maps 1:1 from 0 to KERNLOAD and beyond. If we wanted to move KERNLOAD up to, say, 16 MB, that would suck up a lot of KVA to do so. Perhaps we could make KERNBASE only map 1:1 for the first meg or so and then have it "jump" up to KERNLOAD for the second meg. Peter might be a better person to ask. -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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