measuring memory pressure, expose freepages and zone watermarks under /proc perhaps?

[Buddy Lumpkin]

Hi All,

Would it be possible to expose the value of the zone watermarks and
freepages for each zone under /proc in order to present a clear
picture of what the memory pressure on a system looks like?

Running: watch -n1 cat /proc/meminfo,  you can get a pretty good feel
for how much memory pressure each zone is under by watching HighFree
and LowFree fall to a certain point, and then increase in a cyclical
fashion, but it would be absolutely wonderful if some metrics could be
exposed that give us a better view into the amount of memory pressure
a system is under.

In my case, I would like to write an agent that distills this
information in a way that allows users to set alarm thresholds for
their applications. The allocstall metric in /proc/vmstat is nice for
indicating whether a 2.6 kernel has fallen under extreme memory
pressure, but I have applications that are affected noticeably by even
modest amounts of memory pressure make a very noticeable difference in
latency.

Lastly, if anyone knows of a good method for measuring various levels
of memory pressure on 2.4 and/or 2.6 kernels, please share them.

Thanks in advance,

--Buddy
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