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From:   Matteo Croce <mcroce@linux.microsoft.com>
To:     netdev@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org,
        Jonathan Lemon <jonathan.lemon@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Lorenzo Bianconi <lorenzo@kernel.org>,
        Saeed Mahameed <saeedm@nvidia.com>,
        David Ahern <dsahern@gmail.com>,
        Saeed Mahameed <saeed@kernel.org>, Andrew Lunn <andrew@lunn.ch>
Subject: [PATCH net-next 1/6] xdp: reduce size of struct xdp_mem_info
Date:   Mon, 22 Mar 2021 18:02:56 +0100
Message-Id: <20210322170301.26017-2-mcroce@linux.microsoft.com>
In-Reply-To: <20210322170301.26017-1-mcroce@linux.microsoft.com>
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From: Jesper Dangaard Brouer <brouer@redhat.com>

It is possible to compress/reduce the size of struct xdp_mem_info.
This change reduce struct xdp_mem_info from 8 bytes to 4 bytes.

The member xdp_mem_info.id can be reduced to u16, as the mem_id_ht
rhashtable in net/core/xdp.c is already limited by MEM_ID_MAX=0xFFFE
which can safely fit in u16.

The member xdp_mem_info.type could be reduced more than u16, as it stores
the enum xdp_mem_type, but due to alignment it is only reduced to u16.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/net/xdp.h | 4 ++--
 net/core/xdp.c    | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index a5bc214a49d9..c35864d59113 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -48,8 +48,8 @@ enum xdp_mem_type {
 #define XDP_XMIT_FLAGS_MASK	XDP_XMIT_FLUSH
 
 struct xdp_mem_info {
-	u32 type; /* enum xdp_mem_type, but known size type */
-	u32 id;
+	u16 type; /* enum xdp_mem_type, but known size type */
+	u16 id;
 };
 
 struct page_pool;
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 05354976c1fc..3dd47ed83778 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -35,11 +35,11 @@ static struct rhashtable *mem_id_ht;
 
 static u32 xdp_mem_id_hashfn(const void *data, u32 len, u32 seed)
 {
-	const u32 *k = data;
-	const u32 key = *k;
+	const u16 *k = data;
+	const u16 key = *k;
 
 	BUILD_BUG_ON(sizeof_field(struct xdp_mem_allocator, mem.id)
-		     != sizeof(u32));
+		     != sizeof(u16));
 
 	/* Use cyclic increasing ID as direct hash key */
 	return key;
@@ -49,7 +49,7 @@ static int xdp_mem_id_cmp(struct rhashtable_compare_arg *arg,
 			  const void *ptr)
 {
 	const struct xdp_mem_allocator *xa = ptr;
-	u32 mem_id = *(u32 *)arg->key;
+	u16 mem_id = *(u16 *)arg->key;
 
 	return xa->mem.id != mem_id;
 }
-- 
2.30.2