Date: Mon, 08 Jan 1996 14:59:41 -0800 From: David Greenman <davidg@Root.COM> To: Terry Lambert <terry@lambert.org> Cc: gpalmer@westhill.cdrom.com, wosch@cs.tu-berlin.de, hackers@freebsd.org Subject: Re: large files Message-ID: <199601082259.OAA04671@corbin.Root.COM> In-Reply-To: Your message of "Mon, 08 Jan 96 15:41:36 MST." <199601082241.PAA10640@phaeton.artisoft.com>
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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. >> > >> >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. >> >> This is absolutely, 100% wrong. It does NOT work like that. > >Actually, John says it does. As I stated in my followup to John, I >screwed up SHMEM and SHLIB thikning about mmap() as the underlying >implementation mechanism. You made two mistakes. The first one was confusing SHMEM as using mmap() and the second was mis-representing mmap() as requiring large amounts of kernel VM. The problem I have with this is not the mistake (we're human and I make mistakes just like anyone else), but the way in which it was presented as 'fact' and 'authoritative'. If you don't actually _know_ how something works, please do us all a favor and stop saying that you do. You may or may not realize this, but misrepresenting things has a life that goes beyond the error. I spend *too* much time as it is correcting incorrect things that people heard from you in the past. The problem is that many people don't know enough about the underlying systems to determine whether or not something you say is correct (in some cases even I don't know enough about them), so they do what most people do and look at how you are saying it, rather than what you are saying. "Herein lies the problem". -DG David Greenman Core Team/Principal Architect, The FreeBSD Project
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