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kern/39242: NetBSD 4.0 will start busy-loop an hang on machines with more than 4 GB memory

>Number:         39242
>Category:       kern
>Synopsis:       NetBSD 4.0 will start busy-loop an hang on machines with more 
>than 4 GB memory
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jul 28 21:10:00 +0000 2008
>Originator:     Wolfgang Stukenbrock
>Release:        NetBSD 4.0_STABLE
Dr. Nagler & Company GmbH
System: NetBSD s040 4.0_STABLE NetBSD 4.0_STABLE (NSW-S040) #7: Fri Jul 25 
16:02:03 CEST 2008 root@s040:/usr/src/sys/arch/amd64/compile/NSW-S040 amd64
Architecture: x86_64
Machine: amd64
        After 4 GB main memory is used by the system, allocating another 
physical page fails,
        the pagedeamon is kicked, but there is about 3,9 GB free memory - 
according to the statistic - and
        th pagedeamon will do nothing.
        The system comes to sudden stop at this point and nothing works anymore.
        Setup a machine with e.g. 8 GB RAM.
        Then either start some large processes (e.g. "dd if=.. of=... 
bs=1024000k") until the need more than
        4 GB memory or unpack large achives into the filesystem so that the 
filesystem cache will eat up
        4 GB memory.
        Run vmstat or top in parallel an you will see that there is something 
around 3,9 GB free memory, but
        it is not allocated for unknown reasons.
        The pagedaemon will show up 100% activity in top (on all CPU's in the 
system after a while) - if top
        still gets updates, until everything freezes.
        I've found no way to get the system out of this state without pressing 
the reset-button.
        not known to me up to now.
        I've tried VMHIST, but that does not realy help ...
        Some additional printouts in the pagedeamon routines show up, that the 
pagedeamon is dooing nothing,
        because there is still enought free physical memory.
        The problem seems to be related to the 4 GB boundary - other systems 
with identical HW but only 4 GB RAM
        doesn't show this behaviour.


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