docs: clarify page pool NAPI consumer requirement

The comment about requirements when to set the NAPI pointer
may not be super clear. Add more words.

Reviewed-by: Nicolai Buchwitz <nb@tipi-net.de>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260526155722.2790742-3-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/Documentation/networking/page_pool.rst b/Documentation/networking/page_pool.rst
index 6e43e1953218385d9de33443cf036c069974842a..5409c68be3fcba367e9ff1454d6c8afd4bf6b71b 100644 (file)
--- a/Documentation/networking/page_pool.rst
+++ b/Documentation/networking/page_pool.rst
@@ -48,13 +48,18 @@ genetlink family (see Documentation/netlink/specs/netdev.yaml).
 
 API interface
 =============
-The number of pools created **must** match the number of hardware queues
+The number of pools created **must** match the number of NAPI contexts / queues
 unless hardware restrictions make that impossible. This would otherwise beat the
 purpose of page pool, which is allocate pages fast from cache without locking.
 This lockless guarantee naturally comes from running under a NAPI softirq.
 The protection doesn't strictly have to be NAPI, any guarantee that allocating
 a page will cause no race conditions is enough.
 
+If ``params.napi`` is set, the NAPI instance must be the sole consumer
+context for pages allocated from the pool. In other words, when running in
+that NAPI context, the page pool may safely access consumer-side resources
+**without any additional locking**.
+
 .. kernel-doc:: net/core/page_pool.c
    :identifiers: page_pool_create
 
@@ -139,7 +144,7 @@ Registration
     pp_params.pool_size = DESC_NUM;
     pp_params.nid = NUMA_NO_NODE;
     pp_params.dev = priv->dev;
-    pp_params.napi = napi; /* only if locking is tied to NAPI */
+    pp_params.napi = napi; /* only if this NAPI is the sole consumer, see above */
     pp_params.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
     page_pool = page_pool_create(&pp_params);