Date: Sun, 16 Aug 1998 08:05:59 -0700 From: David Greenman <dg@root.com> To: Terry Lambert <tlambert@primenet.com> Cc: current@FreeBSD.ORG, karl@mcs.net Subject: Re: Better VM patches (was Tentative fix for VM bug) Message-ID: <199808161506.IAA02398@implode.root.com> In-Reply-To: Your message of "Sun, 16 Aug 1998 14:31:59 -0000." <199808161431.HAA16709@usr08.primenet.com>
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>> >John also suggested another change for detecting a case where page >> >orphans can be created. in vm_page.c, it's possible that an object >> >entry in the page insert function will overwrite an existing entry; >> >I added a DIAGNOSTIC panic to catch this when it happens. >> >> You mean that there can be multiple pages at the same offset? It would >> be bad if that happend, but I'm skeptical that it actually does. > >To elaborate: I think that the behaviour I am seeing in the "mmap'ed >file contents, on a page boundary, written to another file" case is a >result of a single page being in multiple maps. Uh, what does "single page being in multiple maps" mean exactly? What map? Pages belong to objects. A page can belong to only one object (there's only one set of list pointers, so nothing else is possible. :-)). If you see some of one file show up in another, then this suggests to me that a bzero isn't happening when it needs to, resulting in stale cached file data being considered valid. I have a suggestion. Let's not throw out random guesses about what may or may not be a problem. Let's actually understand the issue thoroghly, come up with a fix, and then tell people all about it. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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