netdev - Re: [PATCH net-next v3] lib/rhashtable: allow user to set the minimum shifts of shrinking

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Date:	Mon, 1 Sep 2014 10:03:02 +0100
From:	Thomas Graf <tgraf@...g.ch>
To:	Ying Xue <ying.xue@...driver.com>
Cc:	davem@...emloft.net, eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] lib/rhashtable: allow user to set the
 minimum shifts of shrinking

On 08/30/14 at 02:48pm, Ying Xue wrote:
> Although rhashtable library allows user to specify a quiet big size
> for user's created hash table, the table may be shrunk to a
> very small size - HASH_MIN_SIZE(4) after object is removed from
> the table at the first time. Subsequently, even if the total amount
> of objects saved in the table is quite lower than user's initial
> setting in a long time, the hash table size is still dynamically
> adjusted by rhashtable_shrink() or rhashtable_expand() each time
> object is inserted or removed from the table. However, as
> synchronize_rcu() has to be called when table is shrunk or
> expanded by the two functions, we should permit user to set the
> minimum table size through configuring the minimum number of shifts
> according to user specific requirement, avoiding these expensive
> actions of shrinking or expanding because of calling synchronize_rcu().
> 
> Signed-off-by: Ying Xue <ying.xue@...driver.com>

I see the following warning when compiling:

In file included from lib/rhashtable.c:17:0:
lib/rhashtable.c: In function ‘rhashtable_init’:
include/linux/kernel.h:715:17: warning: comparison of distinct pointer types lacks a cast [enabled by default]
  (void) (&_max1 == &_max2);  \
                 ^
lib/rhashtable.c:570:22: note: in expansion of macro ‘max’
  params->min_shift = max(params->min_shift, ilog2(HASH_MIN_SIZE));
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