[PATCH] struct request: shrink and optimize some more

Move some members around and unionize completion_data and rb_node since
they cannot ever be used at the same time.

Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 13 insertions, 7 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 8a3e309e0842..a1e288069e2e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -211,6 +211,8 @@ struct request {
         struct list_head queuelist;
         struct list_head donelist;
 
+        request_queue_t *q;
+
         unsigned int cmd_flags;
         enum rq_cmd_type_bits cmd_type;
 
@@ -219,12 +221,12 @@ struct request {
          */
 
         sector_t sector;                /* next sector to submit */
+        sector_t hard_sector;           /* next sector to complete */
         unsigned long nr_sectors;       /* no. of sectors left to submit */
+        unsigned long hard_nr_sectors;  /* no. of sectors left to complete */
         /* no. of sectors left to submit in the current segment */
         unsigned int current_nr_sectors;
 
-        sector_t hard_sector;           /* next sector to complete */
-        unsigned long hard_nr_sectors;  /* no. of sectors left to complete */
         /* no. of sectors left to complete in the current segment */
         unsigned int hard_cur_sectors;
 
@@ -232,7 +234,15 @@ struct request {
         struct bio *biotail;
 
         struct hlist_node hash; /* merge hash */
-        struct rb_node rb_node; /* sort/lookup */
+        /*
+         * The rb_node is only used inside the io scheduler, requests
+         * are pruned when moved to the dispatch queue. So let the
+         * completion_data share space with the rb_node.
+         */
+        union {
+                struct rb_node rb_node; /* sort/lookup */
+                void *completion_data;
+        };
 
         /*
          * two pointers are available for the IO schedulers, if they need
@@ -241,8 +251,6 @@ struct request {
         void *elevator_private;
         void *elevator_private2;
 
-        void *completion_data;
-
         struct gendisk *rq_disk;
         unsigned long start_time;
 
@@ -260,8 +268,6 @@ struct request {
 
         unsigned short ioprio;
 
-        request_queue_t *q;
-
         void *special;
         char *buffer;