UDP memory accounting and limitation (take 12)

Hello,

This is the latest patch set of UDP memory accounting and limitation.

I split my patch set into accounting interface consolidation and UDP memory accounting support. This patch set implements UDP memory accounting support.

To use consolidated accounting functions, I matched format of udp_mem sysctl with tcp_mem. UDP IPv6 is finally supported.

However, currently, only receive buffer accounting is implemented.

The patch set was tested on net-2.6.25 tree.

Changelog take 11 -> take 12:
* split into accounting interface consolidation and UDP memory accounting support.
* used new accounting interface
* supported IPv6
* dropped send buffer accounting

Changelog take 10 -> take 11:
* stoped using spin lock in memory accounting function
* socket lock and backlog processing were used to avoid conflict between receive system call processing and BH
* revised memory accounting functions
* stooped changing sock_queue_rcv_skb() and skb_set_owner_r()
* added __udp_queue_rcv_skb to set proper destructor
* removed udp_set_owner_r()
* removed reclaim in inet_sock_destruct()

Changelog take 9 -> take 10:
* supported using sk_forward_alloc
* introduced several memory accounting functions with spin lock
* changed detagram receive functions to be able to customize destructor
* fixed accounting bugs in previous takes

Best regards,
Hideo Aoki

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Hitachi Computer Products (America) Inc.