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Date: Mon, 06 Jan 2003 04:16:31 -0800
From: Andrew Morton <akpm@digeo.com>
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To: "Stephen C. Tweedie" <sct@redhat.com>
CC: Joe Korty <joe.korty@ccur.com>, Andreas Dilger <adilger@clusterfs.com>,
       rusty@rustcorp.com.au, riel@conectiva.com.br,
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Subject: Re: 2.4.21-pre2 stalls out when running unixbench
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"Stephen C. Tweedie" wrote:
> 
> Hi,
> 
> On Sat, 2003-01-04 at 11:11, Andrew Morton wrote:
> 
> > This is because of differences in how sync() is handled between 2.4.20's
> > ext3 and 2.4.21-pre2's.
> >
> > 2.4.21-pre2:
> >
> >   sync() will start the commit, and will wait on it.  So you know that
> >   when it returns, everything which was dirty is now tight on disk.
> >
> > So yes, running a looping sync while someone else is writing stuff
> > will take much longer in 2.4.21-pre2, because that kernel actually
> > waits on the writeout.
> 
> Actually, I'm wondering if we should back that particular bit out.  For
> a user with a hundred mounted filesystems, syncing each one in order,
> sequentially, is going to suck (and we don't currently have a simple way
> in 2.4 to detect which syncs are on separate spindles and so can be
> parallelised.)
> 

Well personally I prefer slow-and-safe.  But we could make 2.4
do what 2.5 is doing - one pass through the superblocks to start
the syncs and a second pass to wait on them all.

This is fragile stuff though....
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