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Re: Re: RE:Re: RE:How to decide mode and journal size?



On Wed, Apr 03, 2002 at 02:23:01PM +0200, Diego SANTA CRUZ wrote:
> On Wed, 2002-04-03 at 11:21, Andreas Dilger wrote:
> [snip]
> >  Note that it is possible for the entire
> > journal to be pinned in memory, so if you make the journal too large,
> > you may have memory problems.
> > 
> 
> Interesting point!
> 
> How is this affected if there are several ext3 filesystems mounted? Can
> all journals be resident in memory at a time?
>
> I have 5 ext3 filesystems, 4 of them with a 32MB journal, and one with a
> 1MB journal (small /boot partition). Does this mean that I can have 129
> MB of memory used by the ext3 journals?

Yes. If your system is IO stressed and the VM doesn't think you need that
memory for other purposes.

> Since this is a laptop (256 MB) and normally there is not that much fs
> activity (although sometimes I do really stress it), is it advisable to
> reduce the journal size to avoid the above problem (if it is a problem
> that is)?

Not really.  When the journal gets about 50% full, it will force everything
else to wait while it finishes emptying the journal.

With writeback, and ordered mode that would be a hard task to fill the
journal up to 50%, but with data=journal mode it is quite easy.

Mike





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