| Message ID | 1409129851-11630-1-git-send-email-ying.xue@windriver.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
On 08/27/14 at 04:57pm, Ying Xue wrote: > diff --git a/lib/rhashtable.c b/lib/rhashtable.c > index a2c7881..1466e2d 100644 > --- a/lib/rhashtable.c > +++ b/lib/rhashtable.c > @@ -293,12 +293,15 @@ EXPORT_SYMBOL_GPL(rhashtable_expand); > int rhashtable_shrink(struct rhashtable *ht, gfp_t flags) > { > struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht); > + size_t min_shift = ilog2(HASH_MIN_SIZE); > struct rhash_head __rcu **pprev; > unsigned int i; > > ASSERT_RHT_MUTEX(ht); > > - if (tbl->size <= HASH_MIN_SIZE) > + if (ht->p.min_shift) > + min_shift = max(ht->p.min_shift, min_shift); > + if (ht->shift <= min_shift) > return 0; I like it. Can you translate HASH_MIN_SIZE to .minshift in rhashtable_init()? That way we only have to deal with .min_shift in rhashtable_shrink(). Note that shrinking can also be disabled by not providing a .shrink_decision function in rhashtable_params if the shrinking is too expensive for your case. > -static size_t rounded_hashtable_size(unsigned int nelem) > +static size_t rounded_hashtable_size(struct rhashtable_params *params) > { > - return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE); > + size_t size = HASH_MIN_SIZE; > + > + if (params->min_shift) > + size = max((1UL << params->min_shift), HASH_MIN_SIZE); > + > + return max(roundup_pow_of_two(params->nelem_hint * 4 / 3), size); > } Same here. If you merge the provided .min_shift with HASH_MIN_SIZE in rhashtable_init() before calculating the size, the above logic can be simplified a lot. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 08/27/2014 06:34 PM, Thomas Graf wrote: > On 08/27/14 at 04:57pm, Ying Xue wrote: >> diff --git a/lib/rhashtable.c b/lib/rhashtable.c >> index a2c7881..1466e2d 100644 >> --- a/lib/rhashtable.c >> +++ b/lib/rhashtable.c >> @@ -293,12 +293,15 @@ EXPORT_SYMBOL_GPL(rhashtable_expand); >> int rhashtable_shrink(struct rhashtable *ht, gfp_t flags) >> { >> struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht); >> + size_t min_shift = ilog2(HASH_MIN_SIZE); >> struct rhash_head __rcu **pprev; >> unsigned int i; >> >> ASSERT_RHT_MUTEX(ht); >> >> - if (tbl->size <= HASH_MIN_SIZE) >> + if (ht->p.min_shift) >> + min_shift = max(ht->p.min_shift, min_shift); >> + if (ht->shift <= min_shift) >> return 0; > > I like it. Can you translate HASH_MIN_SIZE to .minshift in > rhashtable_init()? That way we only have to deal with .min_shift in > rhashtable_shrink(). > Good suggestion! I will change it in next version. > Note that shrinking can also be disabled by not providing a > .shrink_decision function in rhashtable_params if the shrinking is > too expensive for your case. > Yes, I know the rule. But in some case we hope that rhashtable doesn't take such expensive actions like expanding and shrinking when its size is small; meanwhile, when its size is rather big, shrinking is able to de done as usual. In fact, we already published the max_shift to users, allowing them to limit the biggest size of rhashtable. So, exporting min_shift should be reasonable, having users have a chance to specify the smallest size of rhashtable. >> -static size_t rounded_hashtable_size(unsigned int nelem) >> +static size_t rounded_hashtable_size(struct rhashtable_params *params) >> { >> - return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE); >> + size_t size = HASH_MIN_SIZE; >> + >> + if (params->min_shift) >> + size = max((1UL << params->min_shift), HASH_MIN_SIZE); >> + >> + return max(roundup_pow_of_two(params->nelem_hint * 4 / 3), size); >> } > > Same here. If you merge the provided .min_shift with HASH_MIN_SIZE > in rhashtable_init() before calculating the size, the above logic > can be simplified a lot. > Thanks for your suggestion. Regards, Ying > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h index 36826c0..fb298e9d 100644 --- a/include/linux/rhashtable.h +++ b/include/linux/rhashtable.h @@ -44,6 +44,7 @@ struct rhashtable; * @head_offset: Offset of rhash_head in struct to be hashed * @hash_rnd: Seed to use while hashing * @max_shift: Maximum number of shifts while expanding + * @min_shift: Minimum number of shifts while shrinking * @hashfn: Function to hash key * @obj_hashfn: Function to hash object * @grow_decision: If defined, may return true if table should expand @@ -57,6 +58,7 @@ struct rhashtable_params { size_t head_offset; u32 hash_rnd; size_t max_shift; + size_t min_shift; rht_hashfn_t hashfn; rht_obj_hashfn_t obj_hashfn; bool (*grow_decision)(const struct rhashtable *ht, diff --git a/lib/rhashtable.c b/lib/rhashtable.c index a2c7881..1466e2d 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -293,12 +293,15 @@ EXPORT_SYMBOL_GPL(rhashtable_expand); int rhashtable_shrink(struct rhashtable *ht, gfp_t flags) { struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht); + size_t min_shift = ilog2(HASH_MIN_SIZE); struct rhash_head __rcu **pprev; unsigned int i; ASSERT_RHT_MUTEX(ht); - if (tbl->size <= HASH_MIN_SIZE) + if (ht->p.min_shift) + min_shift = max(ht->p.min_shift, min_shift); + if (ht->shift <= min_shift) return 0; ntbl = bucket_table_alloc(tbl->size / 2, flags); @@ -506,9 +509,14 @@ void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash, } EXPORT_SYMBOL_GPL(rhashtable_lookup_compare); -static size_t rounded_hashtable_size(unsigned int nelem) +static size_t rounded_hashtable_size(struct rhashtable_params *params) { - return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE); + size_t size = HASH_MIN_SIZE; + + if (params->min_shift) + size = max((1UL << params->min_shift), HASH_MIN_SIZE); + + return max(roundup_pow_of_two(params->nelem_hint * 4 / 3), size); } /** @@ -567,7 +575,7 @@ int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params) return -EINVAL; if (params->nelem_hint) - size = rounded_hashtable_size(params->nelem_hint); + size = rounded_hashtable_size(params); tbl = bucket_table_alloc(size, GFP_KERNEL); if (tbl == NULL)
Now the resizeable hash table size is allowed to shrink a too smaller size - HASH_MIN_SIZE(4) although users initially specify a rather big size when table is created. Especially when the number of objects saved in the table keeps a small value in comparison with the initial setting of table size during a quite long time, lots of actions of expanding and shrinking are involved with objects being inserted or removed from table. However, as synchronize_rcu() has to be called during expanding and shrinking, these unnecessary actions would seriously hit users' performance. Therefore, we should permit users to set the minimum table size through configuring the minimum of number of shifts when table is created according to users specific requirement. Signed-off-by: Ying Xue <ying.xue@windriver.com> --- include/linux/rhashtable.h | 2 ++ lib/rhashtable.c | 16 ++++++++++++---- 2 files changed, 14 insertions(+), 4 deletions(-)