Re: High load in 2.6.27, NFS / rpcauth_lookup_credcache()?

Trond Myklebust
2008-10-27T15:48:38Z

On Mon, 2008-10-27 at 10:58 +0100, Max Kellermann wrote:
> On 2008/10/24 20:09, Trond Myklebust <trond.myklebust@fys.uio.no> wrote:
> > OK, could you please describe your environment a bit. Do you have lots
> > of different users logged in at the same time, or do you perhaps use
> > newgrp or su to switch uid/gids a lot on your processes?
> > I'm trying to see if there might be a reason for the lookup in the
> > credcache being such a heavy duty operation in your setup.
>
> It's a web server for shared hosting. The web space is mounted via
> NFSv3 from a NetApp. There is a huge number of web sites on this
> cluster. All web sites are owned by the same UID, and the web server
> runs as a different UID (read-only access).
>
> Each time a CGI starts, its uid is changed to the one "owner" UID
> (similar to mod_suexec, but there's only one UID for all customer
> accounts). Each time a CGI starts, its chroot (pivot_root) is
> constructed with several bind mounts (in a separate namespace with
> CLONE_NEWNS).
>
> There are no new users or groups being created. There are only 2 UIDs
> accessing NFS: the webserver (ro) and CGI (rw).

OK. That points a finger at the garbage collector. Does the following
patch help at all?

Cheers
Trond
------------------------------------------------------------------------
From: Trond Myklebust <Trond.Myklebust@netapp.com>
Date: Mon, 27 Oct 2008 11:43:48 -0400
SUNRPC: Fix rpcauth_prune_expired

We need to make sure that we don't remove creds from the cred_unused list
if they are still under the moratorium, or else they will never get
garbage collected.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---

net/sunrpc/auth.c | 16 +++++++++-------
1 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/net/sunrpc/auth.c b/net/sunrpc/auth.c
index 436bf1b..a045a12 100644
--- a/net/sunrpc/auth.c
+++ b/net/sunrpc/auth.c
@@ -228,19 +228,21 @@ static int
rpcauth_prune_expired(struct list_head *free, int nr_to_scan)
{
spinlock_t *cache_lock;
- struct rpc_cred *cred;
+ struct rpc_cred *cred, *next;
unsigned long expired = jiffies - RPC_AUTH_EXPIRY_MORATORIUM;

- while (!list_empty(&cred_unused)) {
- cred = list_entry(cred_unused.next, struct rpc_cred, cr_lru);
+ list_for_each_entry_safe(cred, next, &cred_unused, cr_lru) {
+
+ /* Enforce a 60 second garbage collection moratorium */
+ if (time_in_range(cred->cr_expire, expired, jiffies) &&
+ test_bit(RPCAUTH_CRED_HASHED, &cred->cr_flags) != 0)
+ continue;
+
list_del_init(&cred->cr_lru);
number_cred_unused--;
if (atomic_read(&cred->cr_count) != 0)
continue;
- /* Enforce a 5 second garbage collection moratorium */
- if (time_in_range(cred->cr_expire, expired, jiffies) &&
- test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) != 0)
- continue;
+
cache_lock = &cred->cr_auth->au_credcache->lock;
spin_lock(cache_lock);
if (atomic_read(&cred->cr_count) == 0) {