On Tue 21-10-14 16:43:55, Sasha Levin wrote:
> While the hash function used by the revoke hashtable is good somewhere else,
> it's not really good here.
>
> The default hash shift (8) means that one third of the hashing function
> gets lost (and is undefined anyways (8 - 12 = negative shift)):
>
> "(block << (hash_shift - 12))) & (table->hash_size - 1)"
>
> Instead, just use the kernel's generic hash function that gets used everywhere
> else.
Thanks. Merged to my tree.
Honza
>
> Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
> ---
> fs/jbd/revoke.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/fs/jbd/revoke.c b/fs/jbd/revoke.c
> index 8898bbd..dcead63 100644
> --- a/fs/jbd/revoke.c
> +++ b/fs/jbd/revoke.c
> @@ -93,6 +93,7 @@
> #include <linux/bio.h>
> #endif
> #include <linux/log2.h>
> +#include <linux/hash.h>
>
> static struct kmem_cache *revoke_record_cache;
> static struct kmem_cache *revoke_table_cache;
> @@ -129,15 +130,11 @@ static void flush_descriptor(journal_t *, struct journal_head *, int, int);
>
> /* Utility functions to maintain the revoke table */
>
> -/* Borrowed from buffer.c: this is a tried and tested block hash function */
> static inline int hash(journal_t *journal, unsigned int block)
> {
> struct jbd_revoke_table_s *table = journal->j_revoke;
> - int hash_shift = table->hash_shift;
>
> - return ((block << (hash_shift - 6)) ^
> - (block >> 13) ^
> - (block << (hash_shift - 12))) & (table->hash_size - 1);
> + return hash_32(block, table->hash_shift);
> }
>
> static int insert_revoke_hash(journal_t *journal, unsigned int blocknr,
> --
> 1.7.10.4
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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