Merge branch 'shrink-struct-ubuf_info'

Pavel Begunkov says:

====================
shrink struct ubuf_info

struct ubuf_info is large but not all fields are needed for all
cases. We have limited space in io_uring for it and large ubuf_info
prevents some struct embedding, even though we use only a subset
of the fields. It's also not very clean trying to use this typeless
extra space.

Shrink struct ubuf_info to only necessary fields used in generic paths,
namely ->callback, ->refcnt and ->flags, which take only 16 bytes. And
make MSG_ZEROCOPY and some other users to embed it into a larger struct
ubuf_info_msgzc mimicking the former ubuf_info.

Note, xen/vhost may also have some cleaning on top by creating
new structs containing ubuf_info but with proper types.
====================

Link: https://lore.kernel.org/r/cover.1663892211.git.asml.silence@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index f15d5b62539b..920eb6413fee 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -533,6 +533,13 @@ enum {
 struct ubuf_info {
 	void (*callback)(struct sk_buff *, struct ubuf_info *,
 			 bool zerocopy_success);
+	refcount_t refcnt;
+	u8 flags;
+};
+
+struct ubuf_info_msgzc {
+	struct ubuf_info ubuf;
+
 	union {
 		struct {
 			unsigned long desc;
@@ -545,8 +552,6 @@ struct ubuf_info {
 			u32 bytelen;
 		};
 	};
-	refcount_t refcnt;
-	u8 flags;
 
 	struct mmpin {
 		struct user_struct *user;
@@ -555,6 +560,8 @@ struct ubuf_info {
 };
 
 #define skb_uarg(SKB)	((struct ubuf_info *)(skb_shinfo(SKB)->destructor_arg))
+#define uarg_to_msgzc(ubuf_ptr)	container_of((ubuf_ptr), struct ubuf_info_msgzc, \
+					     ubuf)
 
 int mm_account_pinned_pages(struct mmpin *mmp, size_t size);
 void mm_unaccount_pinned_pages(struct mmpin *mmp);