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Re: journal buffer_credits problem

In message <1064260935 3f6f55477ef6f www mailshell com>, chrisl_ext3_user cli mailshell com writes:
> From Erez Zadok <ezk cs sunysb edu> on 22 Sep 2003:
> > Now, it's quite possible that we're not doing something right in
> > versionfs
> > which messes ext3 up.  We're unable to tickle this assertion directly
> That is very possible. Do you mind show me the related versionfs code?
> Ext3 need to reserve the number of block it need to modify on creating
> the the transaction.
> If your versionfs dirty some block, which I think it will, it need
> to reserved the extra blocks in ext3_journal_start().
> Without doing so can result in the problem you describe.
> > 1. Are there any more known ext3 bugs of the sort that have been
> > reported?
> >    If so, are there fixes anywhere?  (We didn't see anything new wrt
> > ext3 in
> >    the 2.4.23-pre series.)
> I think there is a good chance you did not reserved it right.
> > 
> > FWIW, we're managed to narrow down the problem to the area in our code
> > that
> > uses the sendfile functionality.  We use sendfile inside our file system
> > to
> > make a copy of a file before it'd be modified, for versioning purposes.
> Again, I would like to take a look at your related versionfs change.
> BTW, you might want to post on ext2-devel as well. 
> Regards,
> Chris

Thanks Chris.  We had to first understand what these buffer_credits are.
And we believe we may have fixed the problem (preliminary tests no longer
tickle the problem).  This was due to the way we were nesting another file
creation+write (for the version file) inside a normal prepare/commit write.

I'll let my student Akshat post a more detailed explanation of the fix's


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