From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kara Subject: Re: [PATCH] fs, jbd: use a more generic hash function Date: Wed, 22 Oct 2014 10:02:18 +0200 Message-ID: <20141022080218.GA26827@quack.suse.cz> References: <1413924235-26276-1-git-send-email-sasha.levin@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: akpm@linux-foundation.org, jack@suse.cz, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, a.ryabinin@samsung.com To: Sasha Levin Return-path: Content-Disposition: inline In-Reply-To: <1413924235-26276-1-git-send-email-sasha.levin@oracle.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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 > --- > 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 > #endif > #include > +#include > > 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 SUSE Labs, CR