block: add one-hit cache for disk partition lookup

[linux-2.6-omap-h63xx.git] / block / genhd.c

diff --git a/block/genhd.c b/block/genhd.c
index 2f7feda61e35fc3cfd8dc74264300baeeaa56826..d84a7df1e2a094e663f7e1683bb941f1c3562e2d 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -181,6 +181,12 @@ void disk_part_iter_exit(struct disk_part_iter *piter)
 }
 EXPORT_SYMBOL_GPL(disk_part_iter_exit);
 
+static inline int sector_in_part(struct hd_struct *part, sector_t sector)
+{
+       return part->start_sect <= sector &&
+               sector < part->start_sect + part->nr_sects;
+}
+
 /**
  * disk_map_sector_rcu - map sector to partition
  * @disk: gendisk of interest
@@ -199,16 +205,22 @@ EXPORT_SYMBOL_GPL(disk_part_iter_exit);
 struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
 {
        struct disk_part_tbl *ptbl;
+       struct hd_struct *part;
        int i;
 
        ptbl = rcu_dereference(disk->part_tbl);
 
+       part = rcu_dereference(ptbl->last_lookup);
+       if (part && sector_in_part(part, sector))
+               return part;
+
        for (i = 1; i < ptbl->len; i++) {
-               struct hd_struct *part = rcu_dereference(ptbl->part[i]);
+               part = rcu_dereference(ptbl->part[i]);
 
-               if (part && part->start_sect <= sector &&
-                   sector < part->start_sect + part->nr_sects)
+               if (part && sector_in_part(part, sector)) {
+                       rcu_assign_pointer(ptbl->last_lookup, part);
                        return part;
+               }
        }
        return &disk->part0;
 }
@@ -888,8 +900,11 @@ static void disk_replace_part_tbl(struct gendisk *disk,
        struct disk_part_tbl *old_ptbl = disk->part_tbl;
 
        rcu_assign_pointer(disk->part_tbl, new_ptbl);
-       if (old_ptbl)
+
+       if (old_ptbl) {
+               rcu_assign_pointer(old_ptbl->last_lookup, NULL);
                call_rcu(&old_ptbl->rcu_head, disk_free_ptbl_rcu_cb);
+       }
 }
 
 /**