On Thu, Mar 13, 2025 at 3:47 AM Paolo Abeni pabeni@redhat.com wrote:
On 3/8/25 10:40 PM, Mina Almasry wrote:
Currently net_iovs support only pp ref counts, and do not support a page ref equivalent.
This is fine for the RX path as net_iovs are used exclusively with the pp and only pp refcounting is needed there. The TX path however does not use pp ref counts, thus, support for get_page/put_page equivalent is needed for netmem.
Support get_netmem/put_netmem. Check the type of the netmem before passing it to page or net_iov specific code to obtain a page ref equivalent.
For dmabuf net_iovs, we obtain a ref on the underlying binding. This ensures the entire binding doesn't disappear until all the net_iovs have been put_netmem'ed. We do not need to track the refcount of individual dmabuf net_iovs as we don't allocate/free them from a pool similar to what the buddy allocator does for pages.
This code is written to be extensible by other net_iov implementers. get_netmem/put_netmem will check the type of the netmem and route it to the correct helper:
pages -> [get|put]_page() dmabuf net_iovs -> net_devmem_[get|put]_net_iov() new net_iovs -> new helpers
Signed-off-by: Mina Almasry almasrymina@google.com Acked-by: Stanislav Fomichev sdf@fomichev.me
v5: https://lore.kernel.org/netdev/20250227041209.2031104-2-almasrymina@google.c...
Updated to check that the net_iov is devmem before calling net_devmem_put_net_iov().
Jakub requested that callers of __skb_frag_ref()/skb_page_unref be inspected to make sure that they generate / anticipate skbs with the correct pp_recycle and unreadable setting:
skb_page_unref
- callers that are unreachable for unreadable skbs:
gro_pull_from_frag0, skb_copy_ubufs, __pskb_pull_tail
Why `__pskb_pull_tail` is not reachable? it's called by __pskb_trim(), via skb_condense().
I meant to say "the skb_page_unref call from __skb_pull_tail is not reachable for unreadable skbs". This is because __skb_pull_tail early returns on unreadable skbs.