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Date:   Mon, 4 Mar 2019 20:53:38 -0400
From:   Jason Gunthorpe <>
To:     John Hubbard <>
Cc:     Ira Weiny <>,
        Artemy Kovalyov <>,
        "" <>,
        "" <>,
        Andrew Morton <>,
        LKML <>,
        Doug Ledford <>,
        "" <>
Subject: Re: [PATCH v2] RDMA/umem: minor bug fix and cleanup in error
 handling paths

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


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