linux-kernel - RE: [PATCH 3/4] rhashtable: use bit_spin

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Message-ID: <87470518ac3f4ab28918917401b9313b@AcuMS.aculab.com>
Date:   Tue, 2 Apr 2019 10:11:31 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'NeilBrown' <neilb@...e.com>, Thomas Graf <tgraf@...g.ch>,
        Herbert Xu <herbert@...dor.apana.org.au>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/4] rhashtable: use bit_spin_locks to protect hash
 bucket.

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.

	David

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