linux-kernel - [PATCH] net/mlx5e: Make DEFAULT_FRAG

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Message-ID:
 <MN6PR16MB5450CAF432AE40B2AFA58F61B706A@MN6PR16MB5450.namprd16.prod.outlook.com>
Date: Tue,  2 Sep 2025 21:00:16 +0800
From: Mingrui Cui <mingruic@...look.com>
To: Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leon@...nel.org>,
	Tariq Toukan <tariqt@...dia.com>,
	Mark Bloch <mbloch@...dia.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Mingrui Cui <mingruic@...look.com>,
	netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] net/mlx5e: Make DEFAULT_FRAG_SIZE relative to page size

When page size is 4K, DEFAULT_FRAG_SIZE of 2048 ensures that with 3
fragments per WQE, odd-indexed WQEs always share the same page with
their subsequent WQE. However, this relationship does not hold for page
sizes larger than 8K. In this case, wqe_index_mask cannot guarantee that
newly allocated WQEs won't share the same page with old WQEs.

If the last WQE in a bulk processed by mlx5e_post_rx_wqes() shares a
page with its subsequent WQE, allocating a page for that WQE will
overwrite mlx5e_frag_page, preventing the original page from being
recycled. When the next WQE is processed, the newly allocated page will
be immediately recycled.

In the next round, if these two WQEs are handled in the same bulk,
page_pool_defrag_page() will be called again on the page, causing
pp_frag_count to become negative.

Fix this by making DEFAULT_FRAG_SIZE always equal to half of the page
size.

Signed-off-by: Mingrui Cui <mingruic@...look.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
index 3cca06a74cf9..d96a3cbea23c 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c
@@ -666,7 +666,7 @@ static void mlx5e_rx_compute_wqe_bulk_params(struct mlx5e_params *params,
 	info->refill_unit = DIV_ROUND_UP(info->wqe_bulk, split_factor);
 }

-#define DEFAULT_FRAG_SIZE (2048)
+#define DEFAULT_FRAG_SIZE (PAGE_SIZE / 2)

 static int mlx5e_build_rq_frags_info(struct mlx5_core_dev *mdev,
 				     struct mlx5e_params *params,
-- 
2.43.0