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

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

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.

	Byungchul

---8<---

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;
--

quoted

+
  /**
   * __netmem_address - unsafely get pointer to the memory backing @netmem
   * @netmem: netmem reference to get the pointer for

--
Pavel Begunkov