collectl - Inode Info

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# Inode Monitoring

The name of this subsystem is a slight misnomer because in addition to monitoring inodes it also monitors dentries as well. The information being reported is quite self-explanatory and there should really be no mystery here.

However, it may be worth noting that while inspired by sar -v the information isn't quite the same in case that's what you're expecting. Sar also reports on the number pseudo terminals and somehow that didn't seem to fit with the types of data collectl reports and so was left out.

Another difference worth noting is that while both report the number of open files, actually calling them allocated file handles, it was felt that this number all by itself wasn't providing as much info as it could and so the percentage of the total has also been included in collectl's output.

While I wanted to do the same with dentries, reporting the percentage of the max, I ran into a problem - the number of unused cache entries is wrong, or at least the definition is! Rather than decrease as new directories are created it goes up, which makes no sense to me and so trying to report it as a percentage doesn't seem to make any sense. However, a closer investigation makes me think this is in fact tracking the slab objects named dentry_cache which does increase as new directories are created. However something still isn't quite right because while close, the numbers aren't close enough.

Investigation will continue, though at a lower priority. If/when resolved it will be fixed/documented accordingly.

updated October 17, 2011