[PATCH 6.1.y 05/18] NFSD: Replace nfsd_prune_bucket()

cel
2024-08-10T20:00:48Z

From: Chuck Lever <chuck.lever@oracle.com>

[ Upstream commit a9507f6af1450ed26a4a36d979af518f5bb21e5d ]

Enable nfsd_prune_bucket() to drop the bucket lock while calling
kfree(). Use the same pattern that Jeff recently introduced in the
NFSD filecache.

A few percpu operations are moved outside the lock since they
temporarily disable local IRQs which is expensive and does not
need to be done while the lock is held.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Stable-dep-of: c135e1269f34 ("NFSD: Refactor the duplicate reply cache shrinker")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
fs/nfsd/nfscache.c | 78 +++++++++++++++++++++++++++++++++++++---------
fs/nfsd/trace.h | 22 +++++++++++++
2 files changed, 85 insertions(+), 15 deletions(-)

diff --git a/fs/nfsd/nfscache.c b/fs/nfsd/nfscache.c
index 16e62e92964a..b553f2cece58 100644
--- a/fs/nfsd/nfscache.c
+++ b/fs/nfsd/nfscache.c
@@ -117,6 +117,21 @@ static void nfsd_cacherep_free(struct svc_cacherep *rp)
kmem_cache_free(drc_slab, rp);
}

+static unsigned long
+nfsd_cacherep_dispose(struct list_head *dispose)
+{
+ struct svc_cacherep *rp;
+ unsigned long freed = 0;
+
+ while (!list_empty(dispose)) {
+ rp = list_first_entry(dispose, struct svc_cacherep, c_lru);
+ list_del(&rp->c_lru);
+ nfsd_cacherep_free(rp);
+ freed++;
+ }
+ return freed;
+}
+
static void
nfsd_cacherep_unlink_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
struct svc_cacherep *rp)
@@ -260,6 +275,41 @@ nfsd_cache_bucket_find(__be32 xid, struct nfsd_net *nn)
return &nn->drc_hashtbl[hash];
}

+/*
+ * Remove and return no more than @max expired entries in bucket @b.
+ * If @max is zero, do not limit the number of removed entries.
+ */
+static void
+nfsd_prune_bucket_locked(struct nfsd_net *nn, struct nfsd_drc_bucket *b,
+ unsigned int max, struct list_head *dispose)
+{
+ unsigned long expiry = jiffies - RC_EXPIRE;
+ struct svc_cacherep *rp, *tmp;
+ unsigned int freed = 0;
+
+ lockdep_assert_held(&b->cache_lock);
+
+ /* The bucket LRU is ordered oldest-first. */
+ list_for_each_entry_safe(rp, tmp, &b->lru_head, c_lru) {
+ /*
+ * Don't free entries attached to calls that are still
+ * in-progress, but do keep scanning the list.
+ */
+ if (rp->c_state == RC_INPROG)
+ continue;
+
+ if (atomic_read(&nn->num_drc_entries) <= nn->max_drc_entries &&
+ time_before(expiry, rp->c_timestamp))
+ break;
+
+ nfsd_cacherep_unlink_locked(nn, b, rp);
+ list_add(&rp->c_lru, dispose);
+
+ if (max && ++freed > max)
+ break;
+ }
+}
+
static long prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn,
unsigned int max)
{
@@ -283,11 +333,6 @@ static long prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn,
return freed;
}

-static long nfsd_prune_bucket(struct nfsd_drc_bucket *b, struct nfsd_net *nn)
-{
- return prune_bucket(b, nn, 3);
-}
-
/*
* 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.
@@ -466,6 +511,8 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
__wsum csum;
struct nfsd_drc_bucket *b;
int type = rqstp->rq_cachetype;
+ unsigned long freed;
+ LIST_HEAD(dispose);
int rtn = RC_DOIT;

rqstp->rq_cacherep = NULL;
@@ -490,20 +537,18 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,
found = nfsd_cache_insert(b, rp, nn);
if (found != rp)
goto found_entry;
-
- nfsd_stats_rc_misses_inc();
rqstp->rq_cacherep = rp;
rp->c_state = RC_INPROG;
+ nfsd_prune_bucket_locked(nn, b, 3, &dispose);
+ spin_unlock(&b->cache_lock);

+ freed = nfsd_cacherep_dispose(&dispose);
+ trace_nfsd_drc_gc(nn, freed);
+
+ nfsd_stats_rc_misses_inc();
atomic_inc(&nn->num_drc_entries);
nfsd_stats_drc_mem_usage_add(nn, sizeof(*rp));
-
- nfsd_prune_bucket(b, nn);
-
-out_unlock:
- spin_unlock(&b->cache_lock);
-out:
- return rtn;
+ goto out;

found_entry:
/* We found a matching entry which is either in progress or done. */
@@ -541,7 +586,10 @@ int nfsd_cache_lookup(struct svc_rqst *rqstp, unsigned int start,

out_trace:
trace_nfsd_drc_found(nn, rqstp, rtn);
- goto out_unlock;
+out_unlock:
+ spin_unlock(&b->cache_lock);
+out:
+ return rtn;
}

/**
diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
index 84f26f281fe9..447b3483f94b 100644
--- a/fs/nfsd/trace.h
+++ b/fs/nfsd/trace.h
@@ -1261,6 +1261,28 @@ TRACE_EVENT(nfsd_drc_mismatch,
__entry->ingress)
);

+TRACE_EVENT_CONDITION(nfsd_drc_gc,
+ TP_PROTO(
+ const struct nfsd_net *nn,
+ unsigned long freed
+ ),
+ TP_ARGS(nn, freed),
+ TP_CONDITION(freed > 0),
+ TP_STRUCT__entry(
+ __field(unsigned long long, boot_time)
+ __field(unsigned long, freed)
+ __field(int, total)
+ ),
+ TP_fast_assign(
+ __entry->boot_time = nn->boot_time;
+ __entry->freed = freed;
+ __entry->total = atomic_read(&nn->num_drc_entries);
+ ),
+ TP_printk("boot_time=%16llx total=%d freed=%lu",
+ __entry->boot_time, __entry->total, __entry->freed
+ )
+);
+
TRACE_EVENT(nfsd_cb_args,
TP_PROTO(
const struct nfs4_client *clp,
--
2.45.1