Date: Thu, 9 Apr 2015 10:24:49 -0700 From: Adrian Chadd <adrian@freebsd.org> To: galtsev@kicp.uchicago.edu Cc: =?UTF-8?B?UGllcnJlLVl2ZXMgUMODwqluZWF1?= <pierre-yves.peneau@lip6.fr>, FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: How FreeBSD manage more than 4GB on 32 bits architecture Message-ID: <CAJ-Vmokxmi0Ao_q=3YxB-bNHxEuGb6kFJgjx9=FSjEn2UTk8gw@mail.gmail.com> In-Reply-To: <55353.128.135.70.2.1428598688.squirrel@cosmo.uchicago.edu> References: <5526408F.1090005@asim.lip6.fr> <20150409114941.692910293a8120de4dafd400@yahoo.es> <20150409114906.6dd4379c@archlinux> <55264DC5.9070606@asim.lip6.fr> <55267A63.4040503@qeng-ho.org> <55269509.1080103@asim.lip6.fr> <CAJ-Vmo=e1F1rHRW82r5uwJ5f-vOhZ1qKMbSsM4E0aomzQ=4=UQ@mail.gmail.com> <55353.128.135.70.2.1428598688.squirrel@cosmo.uchicago.edu>
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On 9 April 2015 at 09:58, Valeri Galtsev <galtsev@kicp.uchicago.edu> wrote: > > On Thu, April 9, 2015 11:19 am, Adrian Chadd wrote: >> Hi! >> >> This sounds... very exciting. I'd start by taking a look at how PAE >> works - you may be able to reuse all those pieces and just implement >> more than the 4 bits of physical address space. The interesting bits >> of PAE aren't just the extension of the physical addresses, but all >> the management of mapping things into virtual address space as >> required. > > The only problem with all these exercises is: on 32 bit CPU box a single > process still can only have 4GB of address space (according to my > definitely not deep enough knowledge of kernel)... Well, whatever the kernel/user split is, sure. For some workloads that's fine; you just can't mmap a TB of memory. But there's nothing stopping you mmap'ing windows into a larger physical address space. I've done that before to get around limitations. -adrian
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