netdev - [net-next PATCH RFC 3/8] xdp: reduce size of struct xdp_mem

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Date:   Fri, 07 Dec 2018 00:25:42 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Toke Høiland-Jørgensen <toke@...e.dk>,
        ard.biesheuvel@...aro.org, Jason Wang <jasowang@...hat.com>,
        ilias.apalodimas@...aro.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        w@....eu, Saeed Mahameed <saeedm@...lanox.com>,
        mykyta.iziumtsev@...il.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: [net-next PATCH RFC 3/8] xdp: reduce size of struct xdp_mem_info

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@...hat.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 0f25b3675c5c..5c33b9e0efab 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -46,8 +46,8 @@ 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 4b2b194f4f1f..e79526314864 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -42,11 +42,11 @@ struct xdp_mem_allocator {
 
 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(FIELD_SIZEOF(struct xdp_mem_allocator, mem.id)
-		     != sizeof(u32));
+		     != sizeof(u16));
 
 	/* Use cyclic increasing ID as direct hash key */
 	return key;
@@ -56,7 +56,7 @@ 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;
 }