[PATCH 6/7] nfsd: filecache: change garbage collection to a timer.

[NeilBrown <neilb@suse.de>]

garbage collection never sleeps and no longer walks a list so it runs
quickly only requiring a spinlock.

This means we don't need to use a workqueue, we can use a simple timer
instead.

Rather than taking the lock in the timer callback, which would require
using _bh locking, simply test a flag and wake an nfsd thread.  That
thread checks the flag and ages the lists when needed.

Signed-off-by: NeilBrown <neilb@suse.de>
---
 fs/nfsd/filecache.c | 43 ++++++++++++++++++++++++-------------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 7264faa57280..eb95a53f806f 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -67,10 +67,12 @@ struct nfsd_fcache_disposal {
 	struct list_head older;	/* haven't been used in last 0-2 seconds */
 	struct list_head freeme; /* ready to be discarded */
 	unsigned long num_gc; /* Approximate size of recent plus older */
-	struct delayed_work filecache_laundrette;
+	struct timer_list timer;
 	struct shrinker *file_shrinker;
 	struct nfsd_net *nn;
+	unsigned long flags;
 };
+#define NFSD_FCACHE_DO_AGE	BIT(0)	/* time to age the lists */
 
 static struct kmem_cache		*nfsd_file_slab;
 static struct kmem_cache		*nfsd_file_mark_slab;
@@ -115,8 +117,8 @@ static const struct rhashtable_params nfsd_file_rhash_params = {
 static void
 nfsd_file_schedule_laundrette(struct nfsd_fcache_disposal *l)
 {
-	queue_delayed_work(system_unbound_wq, &l->filecache_laundrette,
-			   NFSD_LAUNDRETTE_DELAY);
+	if (!timer_pending(&l->timer))
+		mod_timer(&l->timer, jiffies + NFSD_LAUNDRETTE_DELAY);
 }
 
 static void
@@ -521,6 +523,19 @@ void nfsd_file_net_dispose(struct nfsd_net *nn)
 {
 	struct nfsd_fcache_disposal *l = nn->fcache_disposal;
 
+	if (test_and_clear_bit(NFSD_FCACHE_DO_AGE, &l->flags)) {
+		spin_lock(&l->lock);
+		list_splice_init(&l->older, &l->freeme);
+		list_splice_init(&l->recent, &l->older);
+		/* We don't know how many were moved to 'freeme' and don't want
+		 * to waste time counting - guess a half.  This is only used
+		 * for the shrinker which doesn't need complete precision.
+		 */
+		l->num_gc /= 2;
+		if (!list_empty(&l->older) || !list_empty(&l->recent))
+			mod_timer(&l->timer, jiffies + NFSD_LAUNDRETTE_DELAY);
+		spin_unlock(&l->lock);
+	}
 	if (!list_empty(&l->freeme)) {
 		LIST_HEAD(dispose);
 		int i;
@@ -557,23 +572,13 @@ void nfsd_file_net_dispose(struct nfsd_net *nn)
 }
 
 static void
-nfsd_file_gc_worker(struct work_struct *work)
+nfsd_file_gc_worker(struct timer_list *t)
 {
 	struct nfsd_fcache_disposal *l = container_of(
-		work, struct nfsd_fcache_disposal, filecache_laundrette.work);
+		t, struct nfsd_fcache_disposal, timer);
 
-	spin_lock(&l->lock);
-	list_splice_init(&l->older, &l->freeme);
-	list_splice_init(&l->recent, &l->older);
-	/* We don't know how many were moved to 'freeme' and don't want
-	 * to waste time counting - guess a half.
-	 */
-	l->num_gc /= 2;
-	if (!list_empty(&l->freeme))
-		svc_wake_up(l->nn->nfsd_serv);
-	if (!list_empty(&l->older) || !list_empty(&l->recent))
-		nfsd_file_schedule_laundrette(l);
-	spin_unlock(&l->lock);
+	set_bit(NFSD_FCACHE_DO_AGE, &l->flags);
+	svc_wake_up(l->nn->nfsd_serv);
 }
 
 static unsigned long
@@ -868,7 +873,7 @@ nfsd_alloc_fcache_disposal(void)
 	if (!l)
 		return NULL;
 	spin_lock_init(&l->lock);
-	INIT_DELAYED_WORK(&l->filecache_laundrette, nfsd_file_gc_worker);
+	timer_setup(&l->timer, nfsd_file_gc_worker, 0);
 	INIT_LIST_HEAD(&l->recent);
 	INIT_LIST_HEAD(&l->older);
 	INIT_LIST_HEAD(&l->freeme);
@@ -891,7 +896,7 @@ nfsd_alloc_fcache_disposal(void)
 static void
 nfsd_free_fcache_disposal(struct nfsd_fcache_disposal *l)
 {
-	cancel_delayed_work_sync(&l->filecache_laundrette);
+	del_timer_sync(&l->timer);
 	shrinker_free(l->file_shrinker);
 	nfsd_file_release_list(&l->recent);
 	WARN_ON_ONCE(!list_empty(&l->recent));
-- 
2.47.1