netdev - RE: [v3 PATCH 9/9] rhashtable: Add immediate rehash during insertion

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CB07C98@AcuExch.aculab.com>
Date:	Mon, 23 Mar 2015 16:54:22 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Thomas Graf' <tgraf@...g.ch>,
	Herbert Xu <herbert@...dor.apana.org.au>
CC:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Patrick McHardy <kaber@...sh.net>,
	Josh Triplett <josh@...htriplett.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [v3 PATCH 9/9] rhashtable: Add immediate rehash during insertion

From: Thomas Graf
> On 03/24/15 at 12:50am, Herbert Xu wrote:
> > @@ -116,6 +117,7 @@ struct rhashtable_params {
> >  	unsigned int		max_size;
> >  	unsigned int		min_size;
> >  	u32			nulls_base;
> > +	bool			insecure_elasticity;
> >  	size_t			locks_mul;
> >  	rht_hashfn_t		hashfn;
> >  	rht_obj_hashfn_t	obj_hashfn;
> 
> First of all, love the naming of this variable ;-)
> 
> > @@ -127,6 +129,7 @@ struct rhashtable_params {
> >   * @tbl: Bucket table
> >   * @nelems: Number of elements in table
> >   * @key_len: Key length for hashfn
> > + * @elasticity: Maximum chain length before rehash
> >   * @p: Configuration parameters
> >   * @run_work: Deferred worker to expand/shrink asynchronously
> >   * @mutex: Mutex to protect current/future table swapping
> 
> 2nd: Seems like you rely on an underflow to allow to "disable"
> the elasticity limit. Fair enough, but it would be great to
> have the limit configurable as well.
> 
> How about making elasticity a signed int, default to 16 if user
> specifies 0 and require it to be set to -1 (through a define)
> to actually disable the behaviour. That would avoid requiring
> two variables to implement this and makes the limit configurable
> at the same time.

Or set the value to MAXINT to disable it.
That way you don't even need two tests in the code.

	David

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