Date: Thu, 23 Jul 1998 20:54:26 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: tlambert@primenet.com (Terry Lambert) Cc: toasty@home.dragondata.com, current@FreeBSD.ORG Subject: Re: panic: page fault while in kernel mode - from gcc Message-ID: <199807240154.UAA03907@dyson.iquest.net> In-Reply-To: <199807230410.VAA14655@usr05.primenet.com> from Terry Lambert at "Jul 23, 98 04:10:14 am"
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Terry Lambert said: > > >> This seems to indicate that the new process's page directory either hasn't > > >> been allocated yet or went away for some reason. Apparantly one of several > > >> new bugs that John has left us with. > > >> > > > > > >Is there any reason why someone doesn't back out his last few batches of > > >large vm changes? Apparently he was half done with some of it, and what we > > >had before seemed more stable than what we have now. > > > > That may ultimately be what we have to do, but the fixes also fixed some > > serious 'leak' style problems with the Mach derived VM system, so I'd rather > > that we find the bugs and fix them rather than going back to the previous > > code. > > FreeBSD doesn't currently include the batch of patches that Elvind > saved and that John had in his home directory when it was removed, > does it? > > What is the behaviour with those patches added in? > At the end, I was mostly working on the restructuring of the LL stuff to support SMP as well as it could be with a monolithic kernel. Those patches might have some VM fixes in them, but since I left abruptly (for appropriate reasons) the experimental code is probably a little rough. I suggest that the VM traceback that was posted doesn't indicate a severe or subtile problem (other than in the sense of user-inconvienience.) The fix is likely easy, and discussing it by those who might understand the code, takes probably more energy than actually "just making it go away." I don't have a FreeBSD development environment anymore, so those who have one and understand how the code goes together should probably just fix it. (It appears to be a problem with (obviously) vm_map_copy_entry, and the pmap_copy code.) Since it is an unintentional page fault, it is likely a missing page table page. It is either a reference count problem, or a trivial code botch. Remember, that before filling a page table page, it is important that it exist!!! If the problem is being tickled too often, just disable pmap_copy until the problem can be fixed, which is only a code optimization, and the system will likely work fine without it (but without one of the important optimizations, temporarily.) Again, this is only off the top of my head -- I am busy with other kinds of kernel things for now. -- John | Never try to teach a pig to sing, dyson@iquest.net | it makes one look stupid jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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