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Date: Thu, 28 Aug 2014 09:04:17 +0800 From: Ying Xue <ying.xue@...driver.com> To: Thomas Graf <tgraf@...g.ch> CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <netdev@...r.kernel.org> Subject: Re: [PATCH RFC] lib/rhashtable: allow users to set the minimum shifts of shrinking 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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