Hello,
We've noticed that when a namespace has a large amount of IP addresses,
the list `net->sctp.local_addr_list` gets obscenely long.
This list contains both IPv4 and IPv6 addresses, of all scopes, and it is
a single long list, instead of a hashtable.
In our case we had 12K interfaces, each with an IPv4 and 2 IPv6 addresses
(GUA+LLA), which made deletion of a single address pretty expensive, since
it requires a linear search through 36K addresses.
Internally we solved it pretty naively by turning the list into hashmap, which
helped us avoid this bottleneck:
+ #define SCTP_ADDR_HSIZE_SHIFT 8
+ #define SCTP_ADDR_HSIZE (1 << SCTP_ADDR_HSIZE_SHIFT)
- struct list_head local_addr_list;
+ struct list_head local_addr_list[SCTP_ADDR_HSIZE];
I've used the same factor used by the IPv6 & IPv4 address tables.
I am not entirely sure this patch solves a big enough problem for the greater
general kernel community to warrant the increased memory usage (~2KiB-p-netns),
so I'll avoid sending it.
Recently, though, both IPv4 and IPv6 tables were namespacified, which makes
me think that maybe local_addr_list is no longer necessary, enabling us to
them directly instead of maintaining a separate list.
As far as I could tell, the only field of `struct sctp_sockaddr_entry` that
are used for items of this list, aside from the address itself, is the `valid`
bit, which can probably be folded into `struct in_ifaddr` and `struct inet6_ifaddr`.
What I'm suggesting, in short is:
- Represent `valid` inside the original address structs.
- Replace iteration of `local_addr_list` with iteration of ns addr tables
- Eliminate `local_addr_list`
Is this a reasonable proposal?
Thank you for your time,
Gilad
