Some improvements to request deferral and related code

Hi Bruce and all.

When I wrote the authentication cache all those years ago I handled cache misses by arranging to simply retry the whole request, either by saving a copy for be replayed later, or by waiting for the client to resend.

As we know this isn't ideal. Large requests (e.g. writes) don't get saved, TCP connections don't resend in a suitable time, and NFSv4 request are sufficiently complex that restarting from the beginning isn't really a good idea.

So I have finally implemented the "wait a while" approach which has probably been suggested several times and is even implemented in a somewhat hackish way for nfsidmap.

Yes, I know I have probably argued against this in the past. I was wrong.

This series fixes a few little bugs and tidies up some code but does two main important things.

1/ 'allow thread to block....' will wait a little while if there is a cache miss. If an answer is available in that time, it continues on it's merry way. If no answer arrives, the old deferral approach is used. It waits 5 seconds if there are spare nfsd threads, and 1 second if there all threads are busy. I have almost nothing with which to justify these numbers.

2/ 'close connection when...' provides a better fall back for TCP. If the sunrpc layer decides to drop the request without queueing it at all, it will close the connection. This encourages the client to retry sooner.

Please review and comment.

If you like them all, they can be pulled from

      git://neil.brown.name/linux-2.6/ nfsd

Thanks,
NeilBrown

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NeilBrown (12):
sunrpc: close connection when a request is irretrievably lost. sunrpc/cache: change deferred-request hash table to use hlist.
sunrpc: fix memory leak in unix_gid cache.
nfsd/idmap: drop special request deferal in favour of improved default. sunrpc/cache: retry cache lookups that return -ETIMEDOUT sunrpc/cache: allow thread to block while waiting for cache update. sunrpc/cache: avoid variable over-loading in cache_defer_req sunrpc/cache: use list_del_init for the list_head entries in cache_deferred_req sunrpc/cache: recheck cache validity after cache_defer_req sunrpc/cache: simplify cache_fresh_locked and cache_fresh_unlocked. sunrpc/cache: make sure deferred requests eventually get revisited. sunrpc/cache: rename queue_loose to cache_dequeue

 fs/nfsd/export.c               |   18 ++++
 fs/nfsd/nfs4idmap.c            |  105 +++---------------------
 include/linux/sunrpc/cache.h   |    5 +
 include/linux/sunrpc/svcauth.h |   10 ++
 net/sunrpc/cache.c             |  173 ++++++++++++++++++++++++++--------------
 net/sunrpc/svc.c               |    3 +
 net/sunrpc/svc_xprt.c          |   11 +++
 net/sunrpc/svcauth_unix.c      |   31 ++++++-
 8 files changed, 192 insertions(+), 164 deletions(-)