[PATCH 00/12] Some improvements to request deferral and related code

NeilBrown
2009-08-04T05:24:05Z

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(-)

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