Date: Mon, 8 Jan 1996 13:23:31 -0800 (PST) From: John Dyson <dyson> To: terry@lambert.org (Terry Lambert) Cc: gpalmer@westhill.cdrom.com, wosch@cs.tu-berlin.de, hackers@FreeBSD.org Subject: Re: large files Message-ID: <199601082123.NAA09107@freefall.freebsd.org> In-Reply-To: <199601082008.NAA10273@phaeton.artisoft.com> from "Terry Lambert" at Jan 8, 96 01:08:42 pm
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> > I believe the restriction is based on mmap'ed files taking a portion > of the kernel address space equal to their size. This is arguably > a design flaw in the mmap implementation. > Actually, mmap takes almost no kernel VM space. It is our bogus SYSVSHM stuff that takes kernel VM space. > > Really, mmap wants to operate on a demand paged window and arrange > the vnode as the mappable entity so that it can be shared between > various processes without taking kernel address space to do it. > > You need to talk to the VM guys about fixing this. > Hmm... That sounds how it actually works!!! The problem with stuff earlier than current as of about Nov '95 was that a VM object could not be larger than 4GB, and page offsets were represented by a long. We have changed that and now represent the page location inside of an object as a page index. The reason for the 2G limit is that filesystem metadata can reside at negative offsets. We now support a 1Tb limit -- but the retrofit to 2.1 would be very complicated. John Dyson dyson@freebsd.org
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