Re: [PATCH net-next v9 2/8] netmem: introduce utility APIs to use struct netmem_desc

On Mon, Jul 14, 2025 at 10:43:35AM +0100, Pavel Begunkov wrote:

On 7/14/25 00:07, Byungchul Park wrote:

quoted

On Sat, Jul 12, 2025 at 12:59:34PM +0100, Pavel Begunkov wrote:

quoted

On 7/10/25 09:28, Byungchul Park wrote:
...> +

quoted

   static inline struct net_iov *netmem_to_net_iov(netmem_ref netmem)
   {
       if (netmem_is_net_iov(netmem))

@@ -314,6 +340,21 @@ static inline netmem_ref netmem_compound_head(netmem_ref netmem)
       return page_to_netmem(compound_head(netmem_to_page(netmem)));
   }

+#define nmdesc_to_page(nmdesc)               (_Generic((nmdesc),             \
+     const struct netmem_desc * :    (const struct page *)(nmdesc),  \
+     struct netmem_desc * :          (struct page *)(nmdesc)))

Considering that nmdesc is going to be separated from pages and
accessed through indirection, and back reference to the page is
not needed (at least for net/), this helper shouldn't even exist.
And in fact, you don't really use it ...

quoted

+static inline struct netmem_desc *page_to_nmdesc(struct page *page)
+{
+     VM_BUG_ON_PAGE(PageTail(page), page);
+     return (struct netmem_desc *)page;
+}
+
+static inline void *nmdesc_address(struct netmem_desc *nmdesc)
+{
+     return page_address(nmdesc_to_page(nmdesc));
+}

... That's the only caller, and nmdesc_address() is not used, so
just nuke both of them. This helper doesn't even make sense.

Please avoid introducing functions that you don't use as a general
rule.

I'm sorry about making you confused.  I should've included another patch
using the helper like the following.

Ah, I see. And still, it's not a great function. There should be
no way to extract a page or a page address from a nmdesc.

For the diff below it's same as with the mt76 patch, it's allocating
a page, expects it to be a page, using it as a page, but for no reason
keeps it wrapped into netmem. It only adds confusion and overhead.
A rule of thumb would be only converting to netmem if the new code
would be able to work with a netmem-wrapped net_iovs.

Thanks.  I'm now working on this job, avoiding your concern.

By the way, am I supposed to wait for you to complete the work about
extracting type from page e.g. page pool (or bump) type?

	Byungchul

quoted

diff --git a/drivers/net/ethernet/intel/idpf/idpf_txrx.c b/drivers/net/ethernet/intel/idpf/idpf_txrx.c
index cef9dfb877e8..adccc7c8e68f 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_txrx.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_txrx.c

@@ -3266,7 +3266,7 @@ static u32 idpf_rx_hsplit_wa(const struct libeth_fqe *hdr,
                           struct libeth_fqe *buf, u32 data_len)
  {
      u32 copy = data_len <= L1_CACHE_BYTES ? data_len : ETH_HLEN;
-     struct page *hdr_page, *buf_page;
+     struct netmem_desc *hdr_nmdesc, *buf_nmdesc;
      const void *src;
      void *dst;

@@ -3274,10 +3274,10 @@ static u32 idpf_rx_hsplit_wa(const struct libeth_fqe *hdr,
          !libeth_rx_sync_for_cpu(buf, copy))
              return 0;

-     hdr_page = __netmem_to_page(hdr->netmem);
-     buf_page = __netmem_to_page(buf->netmem);
-     dst = page_address(hdr_page) + hdr->offset + hdr_page->pp->p.offset;
-     src = page_address(buf_page) + buf->offset + buf_page->pp->p.offset;
+     hdr_nmdesc = __netmem_to_nmdesc(hdr->netmem);
+     buf_nmdesc = __netmem_to_nmdesc(buf->netmem);
+     dst = nmdesc_address(hdr_nmdesc) + hdr->offset + hdr_nmdesc->pp->p.offset;
+     src = nmdesc_address(buf_nmdesc) + buf->offset + buf_nmdesc->pp->p.offset;

      memcpy(dst, src, LARGEST_ALIGN(copy));
      buf->offset += copy;

--
Pavel Begunkov