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docs: clarify page pool NAPI consumer requirement

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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>
This commit is contained in:
Jakub Kicinski 2026-05-26 08:57:20 -07:00
parent 63c4530050
commit bbf2313cbe
1 changed files with 7 additions and 2 deletions
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9
Documentation/networking/page_pool.rst
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@ -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);