Messages in this thread | | | Date | Fri, 27 Jun 2008 11:52:41 +1000 | From | Dave Chinner <> | Subject | Re: [PATCH 1/6] Extend completions to provide XFS object flush requirements |
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On Thu, Jun 26, 2008 at 01:33:25PM -0700, Daniel Walker wrote: > > On Thu, 2008-06-26 at 14:41 +1000, Dave Chinner wrote: > > XFS object flushing doesn't quite match existing completion semantics. It > > mixed exclusive access with completion. That is, we need to mark an object as > > being flushed before flushing it to disk, and then block any other attempt to > > flush it until the completion occurs. > > > > To do this we introduce: > > > > void init_completion_flush(struct completion *x) > > which initialises x->done = 1 > > > > void completion_flush_start(struct completion *x) > > which blocks if done == 0, otherwise decrements done to zero and > > allows the caller to continue. > > > > bool completion_flush_start_nowait(struct completion *x) > > returns a failure status if done == 0, otherwise decrements done > > to zero and returns a "flush started" status. This is provided > > to allow flushing to begin safely while holding object locks in > > inverted order. > > > > This replaces the use of semaphores for providing this exclusion > > and completion mechanism. > > I think there is some basis to make the changes that you have here. > Specifically this email and thread, > > http://lkml.org/lkml/2008/4/15/232 > > However, I don't like how your implementing this as specifically a > "flush" mechanism for XFS, and the count is limited to just 1 .. There > are several other places that do this kind of counting with semaphores, > and have counts above 1..
Agreed - but the extension has to start somewhere. So, do I simply add a "init_completion_count()" that passes a count value for the completion (i.e. replaces init_completion_flush())?
> > + > > +static inline void completion_flush_start(struct completion *x) > > +{ > > + wait_for_completion(x); > > +} > > Above seems completely pointless.. I would just call > wait_for_completion(), and make the rest of the interface generic.
Except then wait_for_completion_nowait() makes absolutely no sense ;) If i use wait_for_completion() for this, then perhaps the non-blocking version becomes "try_wait_for_completion()". Would this be acceptible?
i.e. the extra functions in the completion API would be:
void init_completion_count(struct completion *x, int count); int try_wait_for_completion(struct completion *x); int completion_in_progress(struct completion *x);
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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