netdev - [PATCH RFC 16/30] NFSD: Fix the filecache LRU shrinker

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Message-ID: <165590727154.75778.8699495406930751112.stgit@manet.1015granger.net>
Date:   Wed, 22 Jun 2022 10:14:31 -0400
From:   Chuck Lever <chuck.lever@...cle.com>
To:     linux-nfs@...r.kernel.org, netdev@...r.kernel.org
Cc:     david@...morbit.com, tgraf@...g.ch, jlayton@...hat.com
Subject: [PATCH RFC 16/30] NFSD: Fix the filecache LRU shrinker

Without LRU item rotation, the shrinker visits only a few items on
the end of the LRU list, and those would always be long-term OPEN
files for NFSv4 workloads. That makes the filecache shrinker
completely ineffective.

Adopt the same strategy as the inode LRU by using LRU_ROTATE.

Suggested-by: Dave Chinner <david@...morbit.com>
Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
---
 fs/nfsd/filecache.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 65085853cc42..deb842f45117 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -453,6 +453,7 @@ nfsd_file_dispose_list_delayed(struct list_head *dispose)
  *
  * Return values:
  *   %LRU_REMOVED: @item was removed from the LRU
+ *   %LRU_ROTATED: @item is to be moved to the LRU tail
  *   %LRU_SKIP: @item cannot be evicted
  */
 static enum lru_status
@@ -491,7 +492,7 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru,
 
 	if (test_and_clear_bit(NFSD_FILE_REFERENCED, &nf->nf_flags)) {
 		trace_nfsd_file_gc_referenced(nf);
-		return LRU_SKIP;
+		return LRU_ROTATE;
 	}
 
 	if (!test_and_clear_bit(NFSD_FILE_HASHED, &nf->nf_flags)) {
@@ -528,13 +529,14 @@ static void nfsd_file_gc_dispose_list(struct list_head *dispose)
 static void
 nfsd_file_gc(void)
 {
+	unsigned long max = list_lru_count(&nfsd_file_lru);
 	LIST_HEAD(dispose);
 	unsigned long ret;
 
 	ret = list_lru_walk(&nfsd_file_lru, nfsd_file_lru_cb,
-			    &dispose, LONG_MAX);
+			    &dispose, max);
 	this_cpu_add(nfsd_file_evictions, ret);
-	trace_nfsd_file_gc_evicted(ret, list_lru_count(&nfsd_file_lru));
+	trace_nfsd_file_gc_evicted(ret, max);
 	nfsd_file_gc_dispose_list(&dispose);
 }