Re: [PATCH 44/51] writeback: implement bdi_wait_for_completion()

[Tejun Heo]

Hello, Jan.

On Wed, Jul 01, 2015 at 06:04:37PM +0200, Jan Kara wrote:
> I'd find it better to extend completions to allow doing what you need. It
> isn't that special. It seems it would be enough to implement
> 
> void wait_for_completions(struct completion *x, int n);
> 
> where @n is the number of completions to wait for. And the implementation
> can stay as is, only in do_wait_for_common() we change checks for x->done ==
> 0 to "x->done < n". That's about it...

I don't know.  While I agree that it'd be nice to have a generic event
count & trigger mechanism in the kernel, I don't think extending
completion is a good idea - the count then works both ways as the
event counter && listener counter and effectively becomes a semaphore
which usually doesn't end well.  There are very few cases where we
want the counter works both ways and I personally think we'd be far
better served if those rare cases implement something custom rather
than generic mechanism becoming cryptic trying to cover everything.

Thanks.

-- 
tejun
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