> From: Tomas Vondra <tv(at)fuzzy(dot)cz>
> But the fluctuation, that surely is strange. What are the page cache
> dirty limits, i.e.
>
> cat /proc/sys/vm/dirty_background_ratio
> cat /proc/sys/vm/dirty_ratio
>
> That's probably #1 source I've seen responsible for such issues (on
> machines with a lot of RAM).
>
+1 on that.
We're running similar 32 core dell servers with H700s and 128Gb RAM.
With those at the defaults (I don't recall if it's 5 and 10 respectively) you're looking at 3.2Gb of dirty pages before pdflush flushes them and 6.4Gb before the process is forced to flush its self.