Date:   Thu, 16 Mar 2023 17:28:42 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     David Howells <dhowells@redhat.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>, Jeff Layton <jlayton@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        Bernard Metzler <bmt@zurich.ibm.com>,
        Tom Talpey <tom@talpey.com>, linux-rdma@vger.kernel.org
Subject: Re: [RFC PATCH 02/28] Add a special allocator for staging netfs
 protocol to MSG_SPLICE_PAGES
Message-ID: <ZBNRysLdgZsfVaSj@casper.infradead.org>
References: <20230316152618.711970-1-dhowells@redhat.com>
 <20230316152618.711970-3-dhowells@redhat.com>
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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?