Messages in this thread | | | Subject | Re: [PATCH 1/6] Extend completions to provide XFS object flush requirements | From | Daniel Walker <> | Date | Thu, 26 Jun 2008 13:33:25 -0700 |
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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..
> + > +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.
Daniel
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