gro: decrease size of CB

The GRO control block (NAPI_GRO_CB) is currently at its maximum size.
This commit reduces its size by putting two groups of fields that are
used only at different times into a union.

Specifically, the fields frag0 and frag0_len are the fields that make up
the frag0 optimisation mechanism, which is used during the initial
parsing of the SKB.

The fields last and age are used after the initial parsing, while the
SKB is stored in the GRO list, waiting for other packets to arrive.

There was one location in dev_gro_receive that modified the frag0 fields
after setting last and age. I changed this accordingly without altering
the code behaviour.

Signed-off-by: Richard Gobert <richardbgobert@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230601161407.GA9253@debian
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/include/net/gro.h b/include/net/gro.h
index a4fab706240d20aee6f46055d5bbaeb397e6ba5c..7b47dd6ce94ff00af946d2813df09018c6dc7db2 100644 (file)
--- a/include/net/gro.h
+++ b/include/net/gro.h
@@ -11,11 +11,23 @@
 #include <net/udp.h>
 
 struct napi_gro_cb {
-       /* Virtual address of skb_shinfo(skb)->frags[0].page + offset. */
-       void    *frag0;
+       union {
+               struct {
+                       /* Virtual address of skb_shinfo(skb)->frags[0].page + offset. */
+                       void    *frag0;
 
-       /* Length of frag0. */
-       unsigned int frag0_len;
+                       /* Length of frag0. */
+                       unsigned int frag0_len;
+               };
+
+               struct {
+                       /* used in skb_gro_receive() slow path */
+                       struct sk_buff *last;
+
+                       /* jiffies when first packet was created/queued */
+                       unsigned long age;
+               };
+       };
 
        /* This indicates where we are processing relative to skb->data. */
        int     data_offset;
@@ -32,9 +44,6 @@ struct napi_gro_cb {
        /* Used in ipv6_gro_receive() and foo-over-udp */
        u16     proto;
 
-       /* jiffies when first packet was created/queued */
-       unsigned long age;
-
 /* Used in napi_gro_cb::free */
 #define NAPI_GRO_FREE             1
 #define NAPI_GRO_FREE_STOLEN_HEAD 2
@@ -77,9 +86,6 @@ struct napi_gro_cb {
 
        /* used to support CHECKSUM_COMPLETE for tunneling protocols */
        __wsum  csum;
-
-       /* used in skb_gro_receive() slow path */
-       struct sk_buff *last;
 };
 
 #define NAPI_GRO_CB(skb) ((struct napi_gro_cb *)(skb)->cb)

diff --git a/net/core/gro.c b/net/core/gro.c
index 6783a47a613666a6dbe58cf124d1ad800e365191..4d45f78e2fac9d1e997dffc34bf3384e310d0382 100644 (file)
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -458,6 +458,14 @@ static void gro_pull_from_frag0(struct sk_buff *skb, int grow)
        }
 }
 
+static void gro_try_pull_from_frag0(struct sk_buff *skb)
+{
+       int grow = skb_gro_offset(skb) - skb_headlen(skb);
+
+       if (grow > 0)
+               gro_pull_from_frag0(skb, grow);
+}
+
 static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
 {
        struct sk_buff *oldest;
@@ -487,7 +495,6 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
        struct sk_buff *pp = NULL;
        enum gro_result ret;
        int same_flow;
-       int grow;
 
        if (netif_elide_gro(skb->dev))
                goto normal;
@@ -562,17 +569,14 @@ found_ptype:
        else
                gro_list->count++;
 
+       /* Must be called before setting NAPI_GRO_CB(skb)->{age|last} */
+       gro_try_pull_from_frag0(skb);
        NAPI_GRO_CB(skb)->age = jiffies;
        NAPI_GRO_CB(skb)->last = skb;
        if (!skb_is_gso(skb))
                skb_shinfo(skb)->gso_size = skb_gro_len(skb);
        list_add(&skb->list, &gro_list->list);
        ret = GRO_HELD;
-
-pull:
-       grow = skb_gro_offset(skb) - skb_headlen(skb);
-       if (grow > 0)
-               gro_pull_from_frag0(skb, grow);
 ok:
        if (gro_list->count) {
                if (!test_bit(bucket, &napi->gro_bitmask))
@@ -585,7 +589,8 @@ ok:
 
 normal:
        ret = GRO_NORMAL;
-       goto pull;
+       gro_try_pull_from_frag0(skb);
+       goto ok;
 }
 
 struct packet_offload *gro_find_receive_by_type(__be16 type)