Re: multi-second freezes with current GIT?

[Mike Galbraith]

On Tue, 2007-05-08 at 18:44 -0700, David Miller wrote:
> I've been noticing this off and on for the past week or so.
> 
> The system seems to jam up for several seconds, anything that would
> need to read from disk just sits there during this time.  I think it's
> correlated with generating a lot of dirty write data.
> 
> My mouse moves around in X etc. so it really is only processes that
> need to read from disk that get stuck.
> 
> Perhaps it's a side effect of those dirty ratio changes Linus made to
> start off the 2.6.22 merge cycle?

Uhoh, that seems highly likely.

I think those changes may have been triggered by my repeatable and truly
horrible system stalls when writing to an ext3 data=ordered nearly full
filesystem.  Anything that does fdatasync() and/or fsync() can cause
very bad experiences indeed.  KDE's little menu/program launcher
doohickey does fdatasync() for some odd reason, which has utterly killed
my entire GUI for up to and including 20 minutes at a whack.

Switching to data=writeback cured those horrors.  Lowering the dirty
ratio reduced the agony of data=ordered tremendously, but didn't make it
even remotely acceptable.

	-Mike

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