[Nagiosplug-devel] [ nagiosplug-Bugs-3552846 ] memory plugin doesn't account for cached memory

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Bugs item #3552846, was opened at 2012-07-31 16:17
Message generated for change (Comment added) made by j-bern
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https://sourceforge.net/tracker/?func=detail&atid=397597&aid=3552846&group_id=29880

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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Cálestyo (calestyo)
Assigned to: Nobody/Anonymous (nobody)
Summary: memory plugin doesn't account for cached memory 

Initial Comment:
Hi.

This is from the old / soon to be disabled again Nagios Plugins bug tracker that used to be at Nagios itself.
I've just copied this bug over. I'm not the original reporter and have no idea about the thoughts about this bug.

This used to be: http://tracker.nagios.org/view.php?id=216
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vdanen:
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keep getting warnings about memory usage on one system (it has 8GB RAM):

WARNING - 397 / 7987 MB (4%) Free Memory, Used: 7590 MB, Shared: 0 MB, Buffers: 813 MB, Cached: 5750 MB

This looks scary, but on a Linux box this is ok. Cached memory is actually a good thing, so while it is technically accurate, it should account for cached memory.

Instead of "Free Memory" it should probably report "Available Memory" in which case it wouldn't be 397MB available but 397MB (free) + 5.7GB (cached) which leaves me with just over 6GB available/usable memory. 


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Comment By: J. Bern (j-bern)
Date: 2012-08-01 09:19

Message:
Unfortunately, things aren't *quite* that simple. While free RAM can be
used immediately and without repercussions, cannibalizing the disk cache
*does* have impact on system performance (namely, increased disk I/O, duh),
including the potential to stop the machine dead in its tracks when the
cache reaches zero.

Also, when asked to provide more RAM to a process, the kernel will actually
decide whether to use ex-disk cache, or swapspace, based on the system's
"swappiness" settings. Hence, for "the full picture", you'ld need to
include swapspace figures as well.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=397597&aid=3552846&group_id=29880