[PATCH v2 6/8] nfsd: add recurring workqueue job to clean the cache

Jeff Layton
2013-02-04T13:18:25Z

It's not sufficient to only clean the cache when requests come in. What
if we have a flurry of activity and then the server goes idle? Add a
workqueue job that will clean the cache every RC_EXPIRE period.

Care is taken to only run this when we expect to have entries expiring.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
fs/nfsd/nfscache.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index e8ea785..d7b088b 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -36,6 +36,7 @@ static inline u32 request_hash(u32 xid)
}

static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
+static void cache_cleaner_func(struct work_struct *unused);

/*
* locking for the reply cache:
@@ -43,6 +44,7 @@ static int nfsd_cache_append(struct svc_rqst *rqstp, struct kvec *vec);
* Otherwise, it when accessing _prev or _next, the lock must be held.
*/
static DEFINE_SPINLOCK(cache_lock);
+static DECLARE_DELAYED_WORK(cache_cleaner, cache_cleaner_func);

/*
* Put a cap on the size of the DRC based on the amount of available
@@ -131,6 +133,8 @@ void nfsd_reply_cache_shutdown(void)
{
struct svc_cacherep *rp;

+ cancel_delayed_work_sync(&cache_cleaner);
+
while (!list_empty(&lru_head)) {
rp = list_entry(lru_head.next, struct svc_cacherep, c_lru);
nfsd_reply_cache_free_locked(rp);
@@ -146,13 +150,15 @@ void nfsd_reply_cache_shutdown(void)
}

/*
- * Move cache entry to end of LRU list
+ * Move cache entry to end of LRU list, and queue the cleaner to run if it's
+ * not already scheduled.
*/
static void
lru_put_end(struct svc_cacherep *rp)
{
rp->c_timestamp = jiffies;
list_move_tail(&rp->c_lru, &lru_head);
+ schedule_delayed_work(&cache_cleaner, RC_EXPIRE);
}

/*
@@ -173,6 +179,42 @@ nfsd_cache_entry_expired(struct svc_cacherep *rp)
}

/*
+ * Walk the LRU list and prune off entries that are older than RC_EXPIRE.
+ * Also prune the oldest ones when the total exceeds the max number of entries.
+ */
+static void
+prune_cache_entries(void)
+{
+ struct svc_cacherep *rp, *tmp;
+
+ list_for_each_entry_safe(rp, tmp, &lru_head, c_lru) {
+ if (!nfsd_cache_entry_expired(rp) &&
+ num_drc_entries <= max_drc_entries)
+ break;
+ nfsd_reply_cache_free_locked(rp);
+ }
+
+ /*
+ * Conditionally rearm the job. If we cleaned out the list, then
+ * cancel any pending run (since there won't be any work to do).
+ * Otherwise, we rearm the job or modify the existing one to run in
+ * RC_EXPIRE since we just ran the pruner.
+ */
+ if (list_empty(&lru_head))
+ cancel_delayed_work(&cache_cleaner);
+ else
+ mod_delayed_work(system_wq, &cache_cleaner, RC_EXPIRE);
+}
+
+static void
+cache_cleaner_func(struct work_struct *unused)
+{
+ spin_lock(&cache_lock);
+ prune_cache_entries();
+ spin_unlock(&cache_lock);
+}
+
+/*
* Search the request hash for an entry that matches the given rqstp.
* Must be called with cache_lock held. Returns the found entry or
* NULL on failure.
@@ -192,7 +234,6 @@ nfsd_cache_search(struct svc_rqst *rqstp)
hlist_for_each_entry(rp, hn, rh, c_hash) {
if (xid == rp->c_xid && proc == rp->c_proc &&
proto == rp->c_prot && vers == rp->c_vers &&
- !nfsd_cache_entry_expired(rp) &&
rpc_cmp_addr(svc_addr(rqstp), (struct sockaddr *)&rp->c_addr) &&
rpc_get_port(svc_addr(rqstp)) == rpc_get_port((struct sockaddr *)&rp->c_addr))
return rp;
@@ -234,8 +275,11 @@ nfsd_cache_lookup(struct svc_rqst *rqstp)
if (!list_empty(&lru_head)) {
rp = list_first_entry(&lru_head, struct svc_cacherep, c_lru);
if (nfsd_cache_entry_expired(rp) ||
- num_drc_entries >= max_drc_entries)
+ num_drc_entries >= max_drc_entries) {
+ lru_put_end(rp);
+ prune_cache_entries();
goto setup_entry;
+ }
}

spin_unlock(&cache_lock);
--
1.7.11.7