Re: [PATCH v2] RDMA/umem: minor bug fix and cleanup in error handling paths

[Jason Gunthorpe]

On Mon, Mar 04, 2019 at 03:11:05PM -0800, John Hubbard wrote:

> get_user_page(): increments page->_refcount by a large amount (1024)
> 
> put_user_page(): decrements page->_refcount by a large amount (1024)
> 
> ...and just stop doing the odd (to me) technique of incrementing once for
> each tail page. I cannot see any reason why that's actually required, as
> opposed to just "raise the page->_refcount enough to avoid losing the head
> page too soon".

I'd very much like to see this in the infiniband umem code - the extra
work and cost of touching every page in a huge page is very much
undesired.

Jason