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

[Matthew Wilcox]

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?