netdev - Re: [ANN] Unified dynamic storage for different socket types instead of separate hash tables.

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Date:	Tue, 27 Mar 2007 17:35:33 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Miller <davem@...emloft.net>,
	shemminger@...ux-foundation.org, netdev@...r.kernel.org
Subject: Re: [ANN] Unified dynamic storage for different socket types instead of separate hash tables.

On Tue, Mar 27, 2007 at 04:23:49PM +0200, Andi Kleen (andi@...stfloor.org) wrote:
> > 2) An extra list insert/delete to give list of all sockets
> 
> That is currently limited by readlock on the hash buckets. I suspect
> any change to a trie with less atomic operations will make it faster.

The best case for trie is to attach a bitmask of used/free slots per
each trie node since it is based on arrays, so that list is not needed
at all. I thought about additional list of all sockets just because I
decided to not drop one of the hlist_node from sock_common, so it could
be reused for other purposes.
That hlist node is used for netlink broadcasting, but netlink case can 
be solved by moving sk_bind_node into private area and drop additional 
8/16 bytes from socket structure.

Trie nodes are protected through RCU, so it is possible to count
not-yet-freed socket as long as miss just-added ones.
I do not think this information can contain anyhow correct information,
since we have essentially the same problem with hash bucket locks -
until bucket is locked, we can not count for just-to-be-added sockets
and count those ones which will be dropped just after lock is released
in case removing function spins/waits for that bucket.

> -Andi

-- 
	Evgeniy Polyakov
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