netdev - [PATCH RFC 05/30] NFSD: Add nfsd_file_lru_dispose

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Message-ID: <165590719916.75778.4838226317826208480.stgit@manet.1015granger.net>
Date:   Wed, 22 Jun 2022 10:13:19 -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 05/30] NFSD: Add nfsd_file_lru_dispose_list() helper

Refactor the invariant part of nfsd_file_lru_walk_list() into a
separate helper function.

Signed-off-by: Chuck Lever <chuck.lever@...cle.com>
---
 fs/nfsd/filecache.c |   29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c
index 6f48528c6284..763a08196dcd 100644
--- a/fs/nfsd/filecache.c
+++ b/fs/nfsd/filecache.c
@@ -457,11 +457,31 @@ nfsd_file_lru_cb(struct list_head *item, struct list_lru_one *lru,
 	return LRU_SKIP;
 }
 
+/*
+ * Unhash items on @dispose immediately, then queue them on the
+ * disposal workqueue to finish releasing them in the background.
+ *
+ * cel: Note that between the time list_lru_shrink_walk runs and
+ * now, these items are in the hash table but marked unhashed.
+ * Why release these outside of lru_cb ? There's no lock ordering
+ * problem since lru_cb currently takes no lock.
+ */
+static void nfsd_file_gc_dispose_list(struct list_head *dispose)
+{
+	struct nfsd_file *nf;
+
+	list_for_each_entry(nf, dispose, nf_lru) {
+		spin_lock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
+		nfsd_file_do_unhash(nf);
+		spin_unlock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
+	}
+	nfsd_file_dispose_list_delayed(dispose);
+}
+
 static unsigned long
 nfsd_file_lru_walk_list(struct shrink_control *sc)
 {
 	LIST_HEAD(head);
-	struct nfsd_file *nf;
 	unsigned long ret;
 
 	if (sc)
@@ -471,12 +491,7 @@ nfsd_file_lru_walk_list(struct shrink_control *sc)
 		ret = list_lru_walk(&nfsd_file_lru,
 				nfsd_file_lru_cb,
 				&head, LONG_MAX);
-	list_for_each_entry(nf, &head, nf_lru) {
-		spin_lock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
-		nfsd_file_do_unhash(nf);
-		spin_unlock(&nfsd_file_hashtbl[nf->nf_hashval].nfb_lock);
-	}
-	nfsd_file_dispose_list_delayed(&head);
+	nfsd_file_gc_dispose_list(&head);
 	return ret;
 }