linux-kernel - [PATCH v4 12/16] fuse: delete dentry if timeout is zero

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Date:   Tue,  3 Sep 2019 13:41:59 +0200
From:   Miklos Szeredi <mszeredi@...hat.com>
To:     virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Vivek Goyal <vgoyal@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: [PATCH v4 12/16] fuse: delete dentry if timeout is zero

Don't hold onto dentry in lru list if need to re-lookup it anyway at next
access.  Only do this if explicitly enabled, otherwise it could result in
performance regression.

More advanced version of this patch would periodically flush out dentries
from the lru which have gone stale.

Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
---
 fs/fuse/dir.c    | 28 +++++++++++++++++++++++++---
 fs/fuse/fuse_i.h |  3 +++
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index dd0f64f7bc06..d44f11ac22ec 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -29,12 +29,28 @@ union fuse_dentry {
 	struct rcu_head rcu;
 };
 
-static inline void fuse_dentry_settime(struct dentry *entry, u64 time)
+static void fuse_dentry_settime(struct dentry *dentry, u64 time)
 {
-	((union fuse_dentry *) entry->d_fsdata)->time = time;
+	struct fuse_conn *fc = get_fuse_conn_super(dentry->d_sb);
+	bool delete = !time && fc->delete_stale;
+	/*
+	 * Mess with DCACHE_OP_DELETE because dput() will be faster without it.
+	 * Don't care about races, either way it's just an optimization
+	 */
+	if ((!delete && (dentry->d_flags & DCACHE_OP_DELETE)) ||
+	    (delete && !(dentry->d_flags & DCACHE_OP_DELETE))) {
+		spin_lock(&dentry->d_lock);
+		if (!delete)
+			dentry->d_flags &= ~DCACHE_OP_DELETE;
+		else
+			dentry->d_flags |= DCACHE_OP_DELETE;
+		spin_unlock(&dentry->d_lock);
+	}
+
+	((union fuse_dentry *) dentry->d_fsdata)->time = time;
 }
 
-static inline u64 fuse_dentry_time(struct dentry *entry)
+static inline u64 fuse_dentry_time(const struct dentry *entry)
 {
 	return ((union fuse_dentry *) entry->d_fsdata)->time;
 }
@@ -255,8 +271,14 @@ static void fuse_dentry_release(struct dentry *dentry)
 	kfree_rcu(fd, rcu);
 }
 
+static int fuse_dentry_delete(const struct dentry *dentry)
+{
+	return time_before64(fuse_dentry_time(dentry), get_jiffies_64());
+}
+
 const struct dentry_operations fuse_dentry_operations = {
 	.d_revalidate	= fuse_dentry_revalidate,
+	.d_delete	= fuse_dentry_delete,
 	.d_init		= fuse_dentry_init,
 	.d_release	= fuse_dentry_release,
 };
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 21a2e86bbdf2..700df42520ec 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -780,6 +780,9 @@ struct fuse_conn {
 	/** Does the filesystem support copy_file_range? */
 	unsigned no_copy_file_range:1;
 
+	/* Delete dentries that have gone stale */
+	unsigned int delete_stale:1;
+
 	/** The number of requests waiting for completion */
 	atomic_t num_waiting;
 
-- 
2.21.0