linux-kernel - Re: [RFC PATCH 02/28] Add a special allocator for staging netfs protocol to MSG_SPLICE

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Message-ID: <ZBNRysLdgZsfVaSj@casper.infradead.org>
Date:   Thu, 16 Mar 2023 17:28:42 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jeff Layton <jlayton@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        netdev@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Bernard Metzler <bmt@...ich.ibm.com>,
        Tom Talpey <tom@...pey.com>, linux-rdma@...r.kernel.org
Subject: 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?