| Message ID | 20230818151220.166215-4-cgzones@googlemail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | [1/6] selinux: print sum of chain lengths^2 for hash tables | expand |
On Fri, Aug 18, 2023 at 11:12 AM Christian Göttsche <cgzones@googlemail.com> wrote: > > The number of buckets is calculated by performing a binary AND against > the mask of the hash table, which is one less than its size (which is a > power of two). This leads to all top bits being discarded, e.g. with > the Reference Policy on Debian there exists 376 entries, leading to a > size of 512, discarding the top 23 bits. > > Use jhash to improve the hash table utilization: > > # current > roletr: 376 entries and 124/512 buckets used, longest chain length 8, sum of chain length^2 1496 > > # patch > roletr: 376 entries and 266/512 buckets used, longest chain length 4, sum of chain length^2 646 > > Signed-off-by: Christian Göttsche <cgzones@googlemail.com> Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
On Aug 18, 2023 =?UTF-8?q?Christian=20G=C3=B6ttsche?= <cgzones@googlemail.com> wrote: > > The number of buckets is calculated by performing a binary AND against > the mask of the hash table, which is one less than its size (which is a > power of two). This leads to all top bits being discarded, e.g. with > the Reference Policy on Debian there exists 376 entries, leading to a > size of 512, discarding the top 23 bits. > > Use jhash to improve the hash table utilization: > > # current > roletr: 376 entries and 124/512 buckets used, longest chain length 8, sum of chain length^2 1496 > > # patch > roletr: 376 entries and 266/512 buckets used, longest chain length 4, sum of chain length^2 646 > > Signed-off-by: Christian Göttsche <cgzones@googlemail.com> > Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com> > --- > security/selinux/ss/policydb.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Merged into selinux/next, thanks. -- paul-moore.com
diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c index 932e383bcad6..dd4a9eff61be 100644 --- a/security/selinux/ss/policydb.c +++ b/security/selinux/ss/policydb.c @@ -491,7 +491,7 @@ static u32 role_trans_hash(const void *k) { const struct role_trans_key *key = k; - return key->role + (key->type << 3) + (key->tclass << 5); + return jhash_3words(key->role, key->type, (u32)key->tclass << 16 | key->tclass, 0); } static int role_trans_cmp(const void *k1, const void *k2)
The number of buckets is calculated by performing a binary AND against the mask of the hash table, which is one less than its size (which is a power of two). This leads to all top bits being discarded, e.g. with the Reference Policy on Debian there exists 376 entries, leading to a size of 512, discarding the top 23 bits. Use jhash to improve the hash table utilization: # current roletr: 376 entries and 124/512 buckets used, longest chain length 8, sum of chain length^2 1496 # patch roletr: 376 entries and 266/512 buckets used, longest chain length 4, sum of chain length^2 646 Signed-off-by: Christian Göttsche <cgzones@googlemail.com> --- security/selinux/ss/policydb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)