On Fri, 10 Aug 2007 22:02:05 +0200, Jan Blunck wrote:
> This patch removes the special round_down() to next power of 2 implementation
> used only at one place in the snapshot target. It is replaced by an equivalent
> 1 << fls() which might use an architecture specific implementation.
>
> Signed-off-by: Jan Blunck <[email protected]>
> ---
> drivers/md/dm-snap.c | 12 +-----------
> 1 file changed, 1 insertion(+), 11 deletions(-)
>
> --- a/drivers/md/dm-snap.c
> +++ b/drivers/md/dm-snap.c
> @@ -333,16 +333,6 @@ static int calc_max_buckets(void)
> }
>
> /*
> - * Rounds a number down to a power of 2.
> - */
> -static uint32_t round_down(uint32_t n)
> -{
> - while (n & (n - 1))
> - n &= (n - 1);
> - return n;
> -}
> -
> -/*
> * Allocate room for a suitable hash table.
> */
> static int init_hash_tables(struct dm_snapshot *s)
> @@ -361,7 +351,7 @@ static int init_hash_tables(struct dm_sn
> hash_size = min(hash_size, max_buckets);
>
> /* Round it down to a power of 2 */
> - hash_size = round_down(hash_size);
> + hash_size = 1 << fls(hash_size);
> if (init_exception_table(&s->complete, hash_size))
> return -ENOMEM;
>
>
Err, this is sooo stupid. First, 1 << fls(n) isn't round down but
roundup_pow_of_2(). Second, hash_size is of type sector_t which could be
u64 with CONFIG_LBD.
--
Subject: dm-snap: Replace special round_down()
This patch removes the special round_down() to next power of 2 implementation
used only at one place in the snapshot target. It is replaced by an equivalent
1 << fls() which might use an architecture specific implementation.
Signed-off-by: Jan Blunck <[email protected]>
---
drivers/md/dm-snap.c | 12 +-----------
1 file changed, 1 insertion(+), 11 deletions(-)
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -333,16 +333,6 @@ static int calc_max_buckets(void)
}
/*
- * Rounds a number down to a power of 2.
- */
-static uint32_t round_down(uint32_t n)
-{
- while (n & (n - 1))
- n &= (n - 1);
- return n;
-}
-
-/*
* Allocate room for a suitable hash table.
*/
static int init_hash_tables(struct dm_snapshot *s)
@@ -361,7 +351,7 @@ static int init_hash_tables(struct dm_sn
hash_size = min(hash_size, max_buckets);
/* Round it down to a power of 2 */
- hash_size = round_down(hash_size);
+ hash_size = 1 << (fls_long(hash_size) - 1);
if (init_exception_table(&s->complete, hash_size))
return -ENOMEM;
-
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