| Message ID | 20240315181414.649045-1-cgzones@googlemail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Paul Moore |
| Headers | show |
| Series | [v2,1/2] selinux: dump statistics for more hash tables | expand |
On Mar 15, 2024 =?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, requiring > for short or similar inputs a hash function with a good avalanche > effect. > > Use djb2a: > > # current > common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11 > classes: 134 entries and 100/256 buckets used, longest chain length 5, sum of chain length^2 234 > roles: 15 entries and 6/16 buckets used, longest chain length 5, sum of chain length^2 57 > types: 4448 entries and 3016/8192 buckets used, longest chain length 41, sum of chain length^2 14922 > users: 7 entries and 3/8 buckets used, longest chain length 3, sum of chain length^2 17 > bools: 306 entries and 221/512 buckets used, longest chain length 4, sum of chain length^2 524 > levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1 > categories: 1024 entries and 400/1024 buckets used, longest chain length 4, sum of chain length^2 2740 > > # patch > common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11 > classes: 134 entries and 101/256 buckets used, longest chain length 3, sum of chain length^2 210 > roles: 15 entries and 9/16 buckets used, longest chain length 3, sum of chain length^2 31 > types: 4448 entries and 3459/8192 buckets used, longest chain length 5, sum of chain length^2 6778 > users: 7 entries and 5/8 buckets used, longest chain length 3, sum of chain length^2 13 > bools: 306 entries and 236/512 buckets used, longest chain length 5, sum of chain length^2 470 > levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1 > categories: 1024 entries and 518/1024 buckets used, longest chain length 7, sum of chain length^2 2992 > > Signed-off-by: Christian Göttsche <cgzones@googlemail.com> > --- > v2: > add licensing note > --- > security/selinux/ss/symtab.c | 22 +++++++++++----------- > 1 file changed, 11 insertions(+), 11 deletions(-) Merged into selinux/dev, thanks. -- paul-moore.com
diff --git a/security/selinux/ss/symtab.c b/security/selinux/ss/symtab.c index c04f8d447873..832660fd84a9 100644 --- a/security/selinux/ss/symtab.c +++ b/security/selinux/ss/symtab.c @@ -12,17 +12,17 @@ static unsigned int symhash(const void *key) { - const char *p, *keyp; - unsigned int size; - unsigned int val; - - val = 0; - keyp = key; - size = strlen(keyp); - for (p = keyp; (p - keyp) < size; p++) - val = (val << 4 | (val >> (8 * sizeof(unsigned int) - 4))) ^ - (*p); - return val; + /* + * djb2a + * Public domain from cdb v0.75 + */ + unsigned int hash = 5381; + unsigned char c; + + while ((c = *(const unsigned char *)key++)) + hash = ((hash << 5) + hash) ^ c; + + return hash; } static int symcmp(const void *key1, const void *key2)
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, requiring for short or similar inputs a hash function with a good avalanche effect. Use djb2a: # current common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11 classes: 134 entries and 100/256 buckets used, longest chain length 5, sum of chain length^2 234 roles: 15 entries and 6/16 buckets used, longest chain length 5, sum of chain length^2 57 types: 4448 entries and 3016/8192 buckets used, longest chain length 41, sum of chain length^2 14922 users: 7 entries and 3/8 buckets used, longest chain length 3, sum of chain length^2 17 bools: 306 entries and 221/512 buckets used, longest chain length 4, sum of chain length^2 524 levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1 categories: 1024 entries and 400/1024 buckets used, longest chain length 4, sum of chain length^2 2740 # patch common prefixes: 7 entries and 5/8 buckets used, longest chain length 2, sum of chain length^2 11 classes: 134 entries and 101/256 buckets used, longest chain length 3, sum of chain length^2 210 roles: 15 entries and 9/16 buckets used, longest chain length 3, sum of chain length^2 31 types: 4448 entries and 3459/8192 buckets used, longest chain length 5, sum of chain length^2 6778 users: 7 entries and 5/8 buckets used, longest chain length 3, sum of chain length^2 13 bools: 306 entries and 236/512 buckets used, longest chain length 5, sum of chain length^2 470 levels: 1 entries and 1/1 buckets used, longest chain length 1, sum of chain length^2 1 categories: 1024 entries and 518/1024 buckets used, longest chain length 7, sum of chain length^2 2992 Signed-off-by: Christian Göttsche <cgzones@googlemail.com> --- v2: add licensing note --- security/selinux/ss/symtab.c | 22 +++++++++++----------- 1 file changed, 11 insertions(+), 11 deletions(-)