geli and BIO_FLUSH and/or BIO_ORDERED issue?

[Pawel Jakub Dawidek]

On Sat, Sep 22, 2012 at 09:48:28PM -0700, John-Mark Gurney wrote:
> Pawel Jakub Dawidek wrote this message on Sat, Sep 22, 2012 at 18:20 +0200:
> > On Tue, Sep 18, 2012 at 09:04:30PM -0700, John-Mark Gurney wrote:
> > > I was looking at geli and I'm not sure if it's implementing BIO_FLUSH
> > > and/or BIO_ORDERED properly...
> > > 
> > > >From my understanding is the BIO_ORDERED is suppose to wait for the
> > > previous _WRITES to complete before returning so that you can ensure
> > > that data is on disk, i.e. _ORDERED is set on a BIO_FLUSH...
> > > 
> > > BIO_ORDERED is handled by diskq_* code such that when you add an _ORDERED
> > > command, all commands are put after it, but there doesn't appear to
> > > be any code to ensure that an _ORDERED command waits for prevoius
> > > pending commands to complete..
> > > 
> > > This is extra obvious in eli in that a _FLUSH is immediately dispatched,
> > > even when there may be _WRITEs that haven't been finished encrypting and
> > > sent down to the disk to get _FLUSHed...
> > > 
> > > Any comments about this?
> > 
> > Hmm, BIO_ORDERED was introduced pretty recently and GEOM classes were
> > not updated to honour it, but it also seems to be to complex to handle
> > in GEOM classes. I wonder if we could hold off new writes and wait for
> > the in-progress writes in GEOM if we spot BIO_ORDERED request without
> > the need to implement this logic in GEOM classes.
> 
> Yeh.  When I was looking at it, it definately seems like it should be
> something that we provide a generic method of handling (as part of
> bioq_*), since all the geom classes need to handle it...

No, in most cases this is not a problem, because most of GEOM classes
just pass all I/O requests without any reordering, so it is enough if
the very last layer (eg. disk driver) handles BIO_ORDERED properly.

I thought what you meant with GELI was that it can reorder writes, for
which it needs more time with BIO_FLUSH requests that it handles
immediately.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
FreeBSD committer                         http://www.FreeBSD.org
Am I Evil? Yes, I Am!                     http://tupytaj.pl
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