On Wed, Sep 02, 2020 at 08:26:42PM +0800, Ming Lei wrote:

'struct percpu_ref' is often embedded into one user structure, and the
instance is usually referenced in fast path, however actually only
'percpu_count_ptr' is needed in fast path.

So move other fields into one new structure of 'percpu_ref_data', and
allocate it dynamically via kzalloc(), then memory footprint of
'percpu_ref' in fast path is reduced a lot and becomes suitable to put
into hot cacheline of user structure.

This looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>