Stephan Uphoff wrote: > Matthew Dillon wrote: > > : > > :> > > :> mmap() and msync(..MS_INVALIDATE..) should work. > > : > > :hmmm that is rather interesting.. > > :I wonder if it would work.... > > :Maybe a vm guru could confirm this.. (under 4.x) > > : > > > > Huh. If I hadn't looked at the code I would have said that > > MS_INVALIDATE doesn't work in FreeBSD, but when I look at the code > > it sure looks like it ought to work! > > > > But, alas, it does not. The invalidation request goes all the way > > through to the vnode pager but it looks like the vnode pager ignores > > it. > > > > MS_INVALIDATE -> OBJPC_INVAL -> VM_PAGER_PUT_INVAL -> IO_INVAL -> (ignored) > > > > IO_INVAL is defined to be 'invalidate after I/O completes', > > not 'throw away the dirty data', but the only place it appears to be > > implemented is in the NFS code. > > > > -Matt > > > 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.
A file with dirty (unflushed) pages. > ( 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 > > > _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
