ridiculous ParNew pause times

[Holger Hoffstätte]

On 04/09/14 18:40, Cornelius Riemenschneider wrote:
> Bingo! First, i tried to get a tool which shows me which process
> writes to which file and how long that takes, but I was unable to
> find one I could master to use. Based on your suggestion I moved the
> log.gc file to a ramdisk and performed extensive load testing - now
> my biggest outlier is 2014-04-09T18:29:13.873+0200: 383.372:
> [GC2014-04-09T18:29:13.874+0200: 383.372: [ParNew:
> 431041K->208698K(3145728K), 1.8312460 secs]
> 11055599K->11203421K(21495808K), 1.8315130 secs] [Times: user=2.61
> sys=0.03, real=1.83 secs] which is okay.

Another idea: are your vm.dirty_(expire|writeback)_centisecs and
especially vm.dirty_(background)_ratio sysctl settings default, aka
ridiculously high? This can result in writeback storms of a huge number
of accumulated dirty buffers and is a common reason for periodic stalls,
which can take forever when another process issues fsync() at
inappropriate moments.

Just a guess.

-h