[PATCH v2 0/1] gro: decrease size of CB

[PATCH v2 0/1] gro: decrease size of CB

[Richard Gobert]

This patch frees up space in the GRO CB, which is currently at its maximum
size. This patch was submitted and reviewed previously in a patch series,
but is now reposted as a standalone patch, as suggested by Paolo.
(https://lore.kernel.org/netdev/889f2dc5e646992033e0d9b0951d5a42f1907e07.camel@redhat.com/)

Changelog:

v1 -> v2:
  * remove inline keyword

Richard Gobert (1):
  gro: decrease size of CB

 include/net/gro.h | 26 ++++++++++++++++----------
 net/core/gro.c    | 18 +++++++++++-------
 2 files changed, 27 insertions(+), 17 deletions(-)

-- 
2.36.1

[PATCH v2 1/1] gro: decrease size of CB

[Richard Gobert]

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>
---
 include/net/gro.h | 26 ++++++++++++++++----------
 net/core/gro.c    | 18 +++++++++++-------
 2 files changed, 27 insertions(+), 17 deletions(-)

diff --git a/include/net/gro.h b/include/net/gro.h
index a4fab706240d..7b47dd6ce94f 100644
--- 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 2d84165cb4f1..c6955ef9ca99 100644
--- a/net/core/gro.c
+++ b/net/core/gro.c
@@ -460,6 +460,14 @@ 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;
@@ -489,7 +497,6 @@ 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;
@@ -564,17 +571,13 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	else
 		gro_list->count++;
 
+	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))
@@ -587,7 +590,8 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 
 normal:
 	ret = GRO_NORMAL;
-	goto pull;
+	gro_try_pull_from_frag0(skb);
+	goto ok;
 }
 
 struct packet_offload *gro_find_receive_by_type(__be16 type)
-- 
2.36.1

Re: [PATCH v2 1/1] gro: decrease size of CB

[Eric Dumazet]

On Wed, May 31, 2023 at 4:30 PM Richard Gobert <richardbgobert@gmail.com> wrote:
>
> 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>
> ---
>  include/net/gro.h | 26 ++++++++++++++++----------
>  net/core/gro.c    | 18 +++++++++++-------
>  2 files changed, 27 insertions(+), 17 deletions(-)
>
> diff --git a/include/net/gro.h b/include/net/gro.h
> index a4fab706240d..7b47dd6ce94f 100644
> --- 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 2d84165cb4f1..c6955ef9ca99 100644
> --- a/net/core/gro.c
> +++ b/net/core/gro.c
> @@ -460,6 +460,14 @@ 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;
> @@ -489,7 +497,6 @@ 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;
> @@ -564,17 +571,13 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
>         else
>                 gro_list->count++;
>

Could you add a comment here or in front of gro_try_pull_from_frag0() ?

/* 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;

Thanks.

Re: [PATCH v2 1/1] gro: decrease size of CB

[Richard Gobert]

> Could you add a comment here or in front of gro_try_pull_from_frag0() ?
> 
> /* Must be called before setting NAPI_GRO_CB(skb)->{age|last} (/

Of Course, I will post a new version with it.