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  • Yes, I guess we could theorize that a very short, sudden burst in memory use which happens in a minute or so, and isn't spotted by Munin could dump the cache, which of course, is spotted because it persists. Commented Oct 25, 2012 at 11:34
  • The header is a bit confusing, in that it's actually showing one week of data, so those are days on the x-as, not weeks. As for the polling frequency: Munin fetches data every 5 minutes, and I don't think that frequency can be altered. I'm only running nginx, mysql, php-fpm and munin-node. Can it have anything to do with the mysql cache, perhaps? Commented Oct 26, 2012 at 20:59
  • I had top (sorted by memory usage) write its output to a file every 5 seconds, then I analyzed that file and found no processes showing any unusual behavior at the point where cached memory suddenly dropped. Unless a process can use this much memory and still escape that 5 second window, I'm not convinced this could be the cause. But if there's no processes running amok, what could it be? Commented Nov 3, 2012 at 10:46
  • This thread is a bit stale, but a quick observation about methodology: how much a process contributes to the system memory cache will not (easily) be reflected in top, since a very active process may pile stuff into the cache very rapidly without its own allocated memory increasing much. For example, reading a very large file in small chunks for transmission -- while the process might never use more than a few MB allocated, those few MB will constantly change and accumulate references in the cache. So the thing to look at in the top output would be a sudden accumulation of CPU time. Commented Dec 6, 2012 at 21:04
  • You might also be interested in this: cognitivedissonance.ca/cogware/plog Commented Dec 6, 2012 at 21:04