Date: Wed, 21 Apr 2004 20:48:40 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Stephan Uphoff <ups@tree.com> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: how to flush out cache.? Message-ID: <200404220348.i3M3merS097986@apollo.backplane.com> References: <200404220152.VAA26897@stups.com>
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:Yes - but FreeBSD then calls vm_object_page_remove to remove the pages :from the vnode object. (vm_object_sync for 5.x or vm_map_clean for 4.x ) : :Mhhh .. 4.X removes the pages without flushing if the file is not write :mapped. :This means that anyone with read access can screw up a file. :( For example periodically throwing away pages from /var/log/wtmp ...) :5.x looks better - but there is a race condition that can cause the same thing. :I think for msync() the vm_object_page_remove() function should be called with :clean_only set to TRUE to avoid throwing away valid changes. :( I will send-pr tomorrow ) : : Stephan I don't quite see that. Could you point out the code in question? (And, of course, a test program would tell us for sure whether that hole exists). There are two different things being removed... the page table entries are removed from pmap via the vm_map for the process, and the pages in the underlying object are being cleaned. Just removing pages from a pmap will not destroy the underlying pages. (I'm not saying that you are wrong, just that we need more information to figure out what is actually happening here). -Matt Matthew Dillon <dillon@backplane.com>
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