On Mon, 2009-04-20 at 11:26 +0200, Jan Kara wrote:
> On Mon 20-04-09 11:07:17, Mike Galbraith wrote:
> > All journal modes seem subject to bad throughput under heavy pressure,
> > though data=ordered seems much less likely to suffer for some reason.
> > Major difference _seems_ to be that write()+largefile induces very much
> > swap activity.
> My rough guess is that this depends on the VM writeout behavior. In
> ordered mode, we forcibly writeout all the dirty data on a transaction
> commit which happens every 5 seconds so they don't accumulate that much.
Aha.
> In other journaling modes we don't do that and decisions about writeout
> (probably how much pdflush manages to write in background vs. how much
> VM throttles the process to do the writeback itself) cause variances in
> the run time. But this is just a guess. You could gather blktraces of
> slow and fast runs and then look if the amount of IO done by different
> processes significantly differs. If Chris has merged by improvements to
> Seekwatcher, then you could nicely visualize this (hmm, that doesn't seem
> to be the case so I'm attaching the diff and a helper script - see comments
> in the beginning of the script and command helps for usage).
Not necessary methinks. Actually _reading_ the proggy instead of just
glancing at it...
@@ -178,7 +178,7 @@ int do_write_chunks(char *target, int *f
unsigned long long remain = len;
char *zeros;
- zeros = calloc(1, len);
+ zeros = calloc(1, data);
I assume that was a booboo.
-Mike
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