On Sat, 2009-01-10 at 12:29 +0900, Ian Kent wrote:
> On Fri, 2009-01-09 at 13:47 -0500, Valerie Aurora Henson wrote:
> > From: Paul Wankadia <[email protected]>
> > Signed-off-by: Valerie Aurora Henson <[email protected]>
>
> Perhaps this will help with the description.
>
> What I think is the main point of this patch is that, with the trivial
> hash function, the length of the chains aren't evenly spread causing
> some chains to be excessively long for large maps. And the size of the
> hash table is too small because for 10000 entries we would have chains
> of about 130 entries if they were in fact spread evenly, and the claim
> is that they aren't.
And, yes, we should also be able to do much better than chain lengths of
around 130.
A simple minded check would be to modify the cache_dump_cache() function
to report chain lengths, add a call to it in a couple of strategic
places and construct a test to load a large map. The difficulty, of
course, is to ensure we are using strings with a distribution of
characters that are really representative of map keys.
>
> > ---
> > include/automount.h | 2 +-
> > lib/cache.c | 29 ++++++++++++++++++-----------
> > 2 files changed, 19 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/automount.h b/include/automount.h
> > index 1ba0d3c..2a082b5 100644
> > --- a/include/automount.h
> > +++ b/include/automount.h
> > @@ -126,7 +126,7 @@ struct autofs_point;
> > #define CHE_DUPLICATE 0x0020
> > #define CHE_UNAVAIL 0x0040
> >
> > -#define HASHSIZE 77
> > +#define HASHSIZE 4096
> > #define NEGATIVE_TIMEOUT 10
> > #define UMOUNT_RETRIES 8
> > #define EXPIRE_RETRIES 3
> > diff --git a/lib/cache.c b/lib/cache.c
> > index ce47e04..36b8294 100644
> > --- a/lib/cache.c
> > +++ b/lib/cache.c
> > @@ -281,20 +281,27 @@ struct mapent_cache *cache_init_null_cache(struct
> > master *master)
> > return mc;
> > }
> >
> > -static unsigned int hash(const char *key)
> > +static u_int32_t hash(const char *key)
> > {
> > - unsigned long hashval;
> > + u_int32_t hashval;
> > char *s = (char *) key;
> >
> > - for (hashval = 0; *s != '\0';)
> > - hashval += *s++;
> > + for (hashval = 0; *s != '\0';) {
> > + hashval += (unsigned char) *s++;
> > + hashval += (hashval << 10);
> > + hashval ^= (hashval >> 6);
> > + }
> > +
> > + hashval += (hashval << 3);
> > + hashval ^= (hashval >> 11);
> > + hashval += (hashval << 15);
> >
> > return hashval % HASHSIZE;
> > }
> >
> > -static unsigned int ino_hash(dev_t dev, ino_t ino)
> > +static u_int32_t ino_hash(dev_t dev, ino_t ino)
> > {
> > - unsigned long hashval;
> > + u_int32_t hashval;
> >
> > hashval = dev + ino;
> >
> > @@ -303,7 +310,7 @@ static unsigned int ino_hash(dev_t dev, ino_t ino)
> >
> > int cache_set_ino_index(struct mapent_cache *mc, const char *key, dev_t
> > dev, ino_t ino)
> > {
> > - unsigned int ino_index = ino_hash(dev, ino);
> > + u_int32_t ino_index = ino_hash(dev, ino);
> > struct mapent *me;
> >
> > me = cache_lookup_distinct(mc, key);
> > @@ -325,7 +332,7 @@ struct mapent *cache_lookup_ino(struct mapent_cache
> > *mc, dev_t dev, ino_t ino)
> > {
> > struct mapent *me = NULL;
> > struct list_head *head, *p;
> > - unsigned int ino_index;
> > + u_int32_t ino_index;
> >
> > ino_index_lock(mc);
> > ino_index = ino_hash(dev, ino);
> > @@ -371,7 +378,7 @@ struct mapent *cache_lookup_first(struct mapent_cache
> > *mc)
> > struct mapent *cache_lookup_next(struct mapent_cache *mc, struct mapent
> > *me)
> > {
> > struct mapent *this;
> > - unsigned long hashval;
> > + u_int32_t hashval;
> > unsigned int i;
> >
> > if (!me)
> > @@ -532,7 +539,7 @@ int cache_add(struct mapent_cache *mc, struct
> > map_source *ms, const char *key, c
> > {
> > struct mapent *me, *existing = NULL;
> > char *pkey, *pent;
> > - unsigned int hashval = hash(key);
> > + u_int32_t hashval = hash(key);
> > int status;
> >
> > me = (struct mapent *) malloc(sizeof(struct mapent));
> > @@ -752,7 +759,7 @@ int cache_update(struct mapent_cache *mc, struct
> > map_source *ms, const char *key
> > int cache_delete(struct mapent_cache *mc, const char *key)
> > {
> > struct mapent *me = NULL, *pred;
> > - unsigned int hashval = hash(key);
> > + u_int32_t hashval = hash(key);
> > int status, ret = CHE_OK;
> > char *this;
> >
>
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