On Fri, Aug 12, 2016 at 12:23:29PM +1000, Dave Chinner wrote:
> Christoph, maybe there's something we can do to only trigger
> speculative prealloc growth checks if the new file size crosses the end of
> the currently allocated block at the EOF. That would chop out a fair
> chunk of the xfs_bmapi_read calls being done in this workload. I'm
> not sure how much effort we should spend optimising this slow path,
> though....

I can look at that, but indeed optimizing this patch seems a bit
stupid.  The other thing we could do is to optimize xfs_bmapi_read - even
if it shouldn't be called this often it seems like it should waste a whole
lot less CPU cycles.