netdev - Re: [PATCH] IPVS: Allow boot time change of hash size.

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Message-Id: <20081126.233758.235891402.davem@davemloft.net>
Date:	Wed, 26 Nov 2008 23:37:58 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	catab@...edromix.ro
Cc:	jmack@...d.net, netdev@...r.kernel.org, lvs-devel@...r.kernel.org
Subject: Re: [PATCH] IPVS: Allow boot time change of hash size.

From: "Catalin(ux) M. BOIE" <catab@...edromix.ro>
Date: Thu, 27 Nov 2008 00:05:50 -0700 (MST)

> Do you mean that it should be computed based on memory size or you mean
> that it should be changeable on-the-fly, even when we have some
> connections in the tables already?

I mean the latter.  We do this in other subsystems, such as
IPSEC, for various hashes.

> Do you have some hints (where to look for a similar thing)?
> The thing that worries me a little is the locking around the move and
> maybe the latency involved. Yes, of course you will not change it several
> times per minute, but...

You only increase, never decrease.

A lock is held during every access to these hash tables, so
the locking should be very similar.

Have a look at xfrm_hash_resize() in net/xfrm/xfrm_state.c to get
a good idea on how this stuff can be done.  And hey, that code
resizes 3 tables at once, you only need to handle one :)
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