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Date: Thu, 02 Aug 2012 15:04:19 +0200
From: Sasha Levin <levinsasha928@gmail.com>
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To: Josh Triplett <josh@joshtriplett.org>
CC: Tejun Heo <tj@kernel.org>, torvalds@linux-foundation.org,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, paul.gortmaker@windriver.com
Subject: Re: [RFC 1/4] hashtable: introduce a small and naive hashtable
References: <20120731182330.GD21292@google.com> <50197348.9010101@gmail.com> <20120801182112.GC15477@google.com> <50197460.8010906@gmail.com> <20120801182749.GD15477@google.com> <50197E4A.7020408@gmail.com> <20120801202432.GE15477@google.com> <5019B0B4.1090102@gmail.com> <20120801224556.GF15477@google.com> <501A4FC1.8040907@gmail.com> <20120802103244.GA23318@leaf> <501A633B.3010509@gmail.com>
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On 08/02/2012 01:23 PM, Sasha Levin wrote:
>> #define DEFINE_HASH_TABLE(name, length) struct hash_table name = { .count = length, .buckets = { [0 ... (length - 1)] = HLIST_HEAD_INIT } }
> The limitation of this approach is that the struct hash_table variable must be 'static', which is a bit limiting - see for example the use of hashtable in 'struct user_namespace'.
> 

What if we just use two possible decelerations? One of static structs and one for regular ones.

struct hash_table {
        size_t bits;
        struct hlist_head buckets[];
};

#define DEFINE_HASHTABLE(name, bits)                                    \
        union {                                                         \
                struct hash_table name;                                 \
                struct {                                                \
                        size_t bits;                                    \
                        struct hlist_head buckets[1 << bits];           \
                } __name;                                               \
        }

#define DEFINE_STATIC_HASHTABLE(name, bit)                              \
        static struct hash_table name = { .bits = bit,                  \
                .buckets = { [0 ... (bit - 1)] = HLIST_HEAD_INIT } }