Re: [RFC PATCH 02/28] Add a special allocator for staging netfs protocol to MSG_SPLICE_PAGES

On Thu, Mar 16, 2023 at 03:25:52PM +0000, David Howells wrote:

If a network protocol sendmsg() sees MSG_SPLICE_DATA, it expects that the
iterator is of ITER_BVEC type and that all the pages can have refs taken on
them with get_page() and discarded with put_page().  Bits of network
filesystem protocol data, however, are typically contained in slab memory
for which the cleanup method is kfree(), not put_page(), so this doesn't
work.

Provide a simple allocator, zcopy_alloc(), that allocates a page at a time
per-cpu and sequentially breaks off pieces and hands them out with a ref as
it's asked for them.  The caller disposes of the memory it was given by
calling put_page().  When a page is all parcelled out, it is abandoned by
the allocator and another page is obtained.  The page will get cleaned up
when the last skbuff fragment is destroyed.

This feels a _lot_ like the page_frag allocator.  Can the two be
unified?