Re: fsync delays for a long time.

[Andrew Morton]

Simon Kirby wrote:
> 
> Not sure if this is related, but I still can't get 2.4 or 2.5 kernels to
> actually read and write at the same time during a large file copy between
> two totally separate devices (eg: from hda1 to hdc1).  "vmstat 1" shows
> reads with no writing for about 6-8 seconds followed by writes with no
> reading for about 5-6 seconds, repeat.

That's different.

It tends to be the case that when the dirty-data-generator hits
a particular threshold, it blocks while we write out vast amounts
of data.  So the throughput is very lumpy.

It's probable that it can be tamed a bit by fiddling with the
/proc/sys/vm/bdflush parameters. 

> Is there a patch available that could fix this?

The -aa patches fiddle extensively with the bdflush thresholds and logic.
There's stuff in there which might addresses this.

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