[PATCH] md: raid0: Replace hash table lookup by looping over all strip_zones.

Andre Noll
2009-05-14T10:43:48Z

The number of strip_zones of a raid0 array is bounded by the number of
drives in the array and is in fact much smaller for typical setups. For
example, any raid0 array containing identical disks will have only
a single strip_zone.

Therefore, the hash tables which are used for quickly finding the
strip_zone that holds a particular sector are of questionable value
and add quite a bit of unnecessary complexity.

This patch replaces the hash table lookup by equivalent code which
simply loops over all strip zones to find the zone that holds the
given sector.

Subsequent cleanup patches will remove the hash table structure.

Signed-off-by: Andre Noll <maan@systemlinux.org>
---
drivers/md/raid0.c | 32 +++++++++++++++++++-------------
1 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index c08d755..9fd3c3c 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -398,6 +398,22 @@ static int raid0_stop (mddev_t *mddev)
return 0;
}

+/* Find the zone which holds a particular offset */
+static struct strip_zone *find_zone(struct raid0_private_data *conf,
+ sector_t sector)
+{
+ int i;
+
+ for (i = 0; i < conf->nr_strip_zones; i++) {
+ struct strip_zone *z = conf->strip_zone + i;
+
+ if (sector < z->zone_start + z->sectors)
+ return z;
+ }
+ BUG();
+ return NULL;
+}
+
static int raid0_make_request (struct request_queue *q, struct bio *bio)
{
mddev_t *mddev = q->queuedata;
@@ -443,20 +459,10 @@ static int raid0_make_request (struct request_queue *q, struct bio *bio)
bio_pair_release(bp);
return 0;
}
-
-
- {
- sector_t x = sector >> conf->sector_shift;
- sector_div(x, (u32)conf->spacing);
- zone = conf->hash_table[x];
- }
-
- while (sector >= zone->zone_start + zone->sectors)
- zone++;
-
+ zone = find_zone(conf, sector);
+ if (!zone)
+ return 1;
sect_in_chunk = bio->bi_sector & (chunk_sects - 1);
-
-
{
sector_t x = (sector - zone->zone_start) >> chunksect_bits;

--
1.5.4.3