Re: [net-next v1 07/16] netdev: netdevice devmem allocator

On Fri, Dec 8, 2023 at 9:56 AM David Ahern [off-list ref] wrote:

On 12/7/23 5:52 PM, Mina Almasry wrote:

quoted

diff --git a/net/core/dev.c b/net/core/dev.c
index b8c8be5a912e..30667e4c3b95 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -2120,6 +2120,41 @@ static int netdev_restart_rx_queue(struct net_device *dev, int rxq_idx)
      return err;
 }

+struct page_pool_iov *netdev_alloc_dmabuf(struct netdev_dmabuf_binding *binding)
+{
+     struct dmabuf_genpool_chunk_owner *owner;
+     struct page_pool_iov *ppiov;
+     unsigned long dma_addr;
+     ssize_t offset;
+     ssize_t index;
+
+     dma_addr = gen_pool_alloc_owner(binding->chunk_pool, PAGE_SIZE,

Any reason not to allow allocation sizes other than PAGE_SIZE? e.g.,
2048 for smaller MTUs or 8192 for larger ones. It can be a property of
page_pool and constant across allocations vs allowing different size for
each allocation.

Only for simplicity. Supporting non-PAGE_SIZE is certainly possible,
but in my estimation it's a huge can of worms worthy of itss own
series. I find this series complicated to implement and review and
support as-is, and if reasonable I would like to punt that as a future
improvement.

At the minimum, I think the needed changes are:

1. The memory provider needs to report to the page pool the alloc size.
2. The page_pool needs to handle non-PAGE_SIZE memory regions.
3. The drivers need to handle non-PAGE_SIZE memory regions. Drivers
today handle fragged pages, but that is different because it's a
PAGE_SIZE region that is fragged. This is a non-PAGE_SIZE region in
the first place.
4. Any PAGE_SIZE assumptions in the entire net stack need to be removed.

At Google we mostly use page aligned MTUs so we're likely not that
interested in sub PAGE_SIZE allocations, but we are interested in n *
PAGE_SIZE allocations, but, I hope, in a separate followup effort.

-- 
Thanks,
Mina