libceph: improve packing in struct ceph_osd_req_op

The layout of struct ceph_osd_req_op leaves lots of holes.
Rearranging things a little for better field alignment
reduces the size by a third.

This resolves:
    http://tracker.ceph.com/issues/4163

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>

1 files changed, 8 insertions, 7 deletions

diff --git a/include/linux/ceph/osd_client.h b/include/linux/ceph/osd_client.h
index 69287ccfe68a..82bf6338d6c1 100644
--- a/include/linux/ceph/osd_client.h
+++ b/include/linux/ceph/osd_client.h
@@ -157,6 +157,7 @@ struct ceph_osd_client {
 
 struct ceph_osd_req_op {
         u16 op;           /* CEPH_OSD_OP_* */
+        u32 payload_len;
         union {
                 struct {
                         u64 offset, length;
@@ -165,23 +166,24 @@ struct ceph_osd_req_op {
                 } extent;
                 struct {
                         const char *name;
-                        u32 name_len;
                         const char  *val;
+                        u32 name_len;
                         u32 value_len;
                         __u8 cmp_op;       /* CEPH_OSD_CMPXATTR_OP_* */
                         __u8 cmp_mode;     /* CEPH_OSD_CMPXATTR_MODE_* */
                 } xattr;
                 struct {
                         const char *class_name;
-                        __u8 class_len;
                         const char *method_name;
-                        __u8 method_len;
-                        __u8 argc;
                         const char *indata;
                         u32 indata_len;
+                        __u8 class_len;
+                        __u8 method_len;
+                        __u8 argc;
                 } cls;
                 struct {
-                        u64 cookie, count;
+                        u64 cookie;
+                        u64 count;
                 } pgls;
                 struct {
                         u64 snapid;
@@ -189,12 +191,11 @@ struct ceph_osd_req_op {
                 struct {
                         u64 cookie;
                         u64 ver;
-                        __u8 flag;
                         u32 prot_ver;
                         u32 timeout;
+                        __u8 flag;
                 } watch;
         };
-        u32 payload_len;
 };
 
 extern int ceph_osdc_init(struct ceph_osd_client *osdc,