Date: Mon, 8 Jan 1996 15:35:46 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: dyson@freefall.freebsd.org (John Dyson) Cc: terry@lambert.org, gpalmer@westhill.cdrom.com, wosch@cs.tu-berlin.de, hackers@FreeBSD.org Subject: Re: large files Message-ID: <199601082235.PAA10623@phaeton.artisoft.com> In-Reply-To: <199601082123.NAA09107@freefall.freebsd.org> from "John Dyson" at Jan 8, 96 01:23:31 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. Oh, duh, pass the hat! I was thinking SHLIB (mmap), but writing about SHMEM. It is, indeed, the SHMEM, not the mmap() stuff that is bogus! > > 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!!! It is. I was reading the code when I wrote that. I just misattributed the code to the wrong subsystem. 8-(. > 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. Yes. He should go to -current if he really needs this. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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