2.6.16-rc5: process with huge vsize but no swap used

[Sanjoy Mahajan]

System is a Thinkpad 600X (Pentium III) w/ 576MB of RAM, 1GB of swap.

While testing 2.6.16-rc5 for ACPI issues, I ran across a vm behavior
that I've never seen before.  I had just booted and logged in via xdm,
and had opened a few small files in emacs.  All of a sudden
sudden emacs complained that:

  Memory exhausted--use M-x save-some-buffers RET

I didn't have any large files opened, but:

$ ps u3817
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
sanjoy    3817  0.1  2.0 1246160 11992 ?       S    Mar09   0:11 emacs -iconic

No swap is being used despite emacs allegedly consuming 1.2GB of VM:

$ free
             total       used       free     shared    buffers     cached
Mem:        580924     219964     360960          0      29124     128956
-/+ buffers/cache:      61884     519040
Swap:      1068280          0    1068280

Is that possible (maybe it's all zero-filled memory)?  If so, it's an
emacs bug that I've never seen before and I'll report it on the emacs
lists.  If it's not possible, then maybe it's a kernel issue.  I saved
/proc/3817/{maps,smaps,status,exe} just in case.

-Sanjoy

`A society of sheep must in time beget a government of wolves.'
   - Bertrand de Jouvenal
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