From: NeilBrown <neilb@suse.com>
To: David Laight <David.Laight@ACULAB.COM>,
Thomas Graf <tgraf@suug.ch>,
Herbert Xu <herbert@gondor.apana.org.au>
Cc: "netdev\@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket.
Date: Wed, 03 Apr 2019 08:10:32 +1100 [thread overview]
Message-ID: <87o95o15br.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <87470518ac3f4ab28918917401b9313b@AcuMS.aculab.com>
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On Tue, Apr 02 2019, David Laight wrote:
> From: NeilBrown
>> Sent: 02 April 2019 00:08
>>
>> This patch changes rhashtables to use a bit_spin_lock on BIT(1) of the
>> bucket pointer to lock the hash chain for that bucket.
> ...
>> To enhance type checking, a new struct is introduced to represent the
>> pointer plus lock-bit
>> that is stored in the bucket-table. This is "struct rhash_lock_head"
>> and is empty. A pointer to this needs to be cast to either an
>> unsigned lock, or a "struct rhash_head *" to be useful.
>> Variables of this type are most often called "bkt".
>
> Did you try using a union of the pointer and an 'unsigned long' ?
> Should remove a lot of the casts.
It might, but I'm not sure it is what we want.
The value is not an unsigned long OR a pointer, it is both blended
together. So it really isn't a union.
We *want* it to require casts to access, so that it is clear that
something unusual is happening, and care is needed.
Thanks,
NeilBrown
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next prev parent reply other threads:[~2019-04-02 21:10 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-01 23:07 [PATCH 0/4 v2] Convert rhashtable to use bitlocks NeilBrown
2019-04-01 23:07 ` [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2019-04-02 10:11 ` David Laight
2019-04-02 21:10 ` NeilBrown [this message]
2019-04-03 9:26 ` David Laight
2019-04-04 0:13 ` NeilBrown
2019-04-08 2:34 ` Herbert Xu
2019-04-10 19:34 ` Guenter Roeck
2019-04-11 0:48 ` NeilBrown
2019-04-11 2:15 ` David Miller
2019-04-11 6:13 ` NeilBrown
2019-04-11 6:40 ` NeilBrown
2019-04-11 12:44 ` Guenter Roeck
2019-04-01 23:07 ` [PATCH 4/4] rhashtable: add lockdep tracking to bucket bit-spin-locks NeilBrown
2019-04-01 23:07 ` [PATCH 2/4] rhashtable: allow rht_bucket_var to return NULL NeilBrown
2019-04-01 23:07 ` [PATCH 1/4] rhashtable: use cmpxchg() in nested_table_alloc() NeilBrown
2019-04-08 2:34 ` Herbert Xu
2019-04-08 2:12 ` [PATCH 0/4 v2] Convert rhashtable to use bitlocks David Miller
2019-04-08 2:35 ` Herbert Xu
-- strict thread matches above, loose matches on Subject: below --
2019-03-25 5:05 [PATCH 0/4] " NeilBrown
2019-03-25 5:05 ` [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2019-03-26 5:03 ` Herbert Xu
2019-03-26 15:36 ` Paul E. McKenney
2019-03-27 3:45 ` Herbert Xu
2019-03-26 22:35 ` NeilBrown
2019-03-27 3:45 ` Herbert Xu
2019-03-27 15:04 ` Paul E. McKenney
2019-03-26 5:27 ` Herbert Xu
2019-03-26 22:40 ` NeilBrown
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