linux-kernel - Re: [PATCH v7 10/16] dlm: use new hashtable implementation

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Message-ID: <20121029162344.GC3516@redhat.com>
Date:	Mon, 29 Oct 2012 12:23:44 -0400
From:	David Teigland <teigland@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	torvalds@...ux-foundation.org, tj@...nel.org,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, paul.gortmaker@...driver.com,
	davem@...emloft.net, rostedt@...dmis.org, mingo@...e.hu,
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	netdev@...r.kernel.org, josh@...htriplett.org,
	eric.dumazet@...il.com, axboe@...nel.dk, agk@...hat.com,
	dm-devel@...hat.com, neilb@...e.de, ccaulfie@...hat.com,
	Trond.Myklebust@...app.com, bfields@...ldses.org,
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	dev@...nvswitch.org, rds-devel@....oracle.com, lw@...fujitsu.com
Subject: Re: [PATCH v7 10/16] dlm: use new hashtable implementation

On Mon, Oct 29, 2012 at 12:07:10PM -0400, Mathieu Desnoyers wrote:
> I'm fine with turning a direct + modulo mapping into a dispersed hash as
> long as there are no underlying assumptions about sequentiality of value
> accesses.
> 
> If the access pattern would happen to be typically sequential, then
> adding dispersion could hurt performances significantly, turning a
> frequent L1 access into a L2 access for instance.
  
> All I'm asking is: have you made sure that this hash table is not
> deliberately kept sequential (without dispersion) to accelerate specific
> access patterns ? This should at least be documented in the changelog.

It was not intentional.  I don't expect any benefit would be lost by
making it non-sequential.

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