From: Ian Kent <raven@themaw.net>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Tejun Heo <tj@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Andrew Morton <akpm@linux-foundation.org>,
Al Viro <viro@ZenIV.linux.org.uk>,
Rick Lindsley <ricklind@linux.vnet.ibm.com>,
David Howells <dhowells@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: [PATCH v2 3/6] kernfs: improve kernfs path resolution
Date: Wed, 17 Jun 2020 15:37:58 +0800 [thread overview]
Message-ID: <159237947839.89469.7331804336434093565.stgit@mickey.themaw.net> (raw)
In-Reply-To: <159237905950.89469.6559073274338175600.stgit@mickey.themaw.net>
Now that an rwsem is used by kernfs, take advantage of it to reduce
lookup overhead.
If there are many lookups (possibly many negative ones) there can
be a lot of overhead during path walks.
To reduce lookup overhead avoid allocating a new dentry where possible.
To do this stay in rcu-walk mode where possible and use the dentry cache
handling of negative hashed dentries to avoid allocating (and freeing
shortly after) new dentries on every negative lookup.
Signed-off-by: Ian Kent <raven@themaw.net>
---
fs/kernfs/dir.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 72 insertions(+), 15 deletions(-)
diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 9b315f3b20ee..f4943329e578 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -1046,15 +1046,75 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
{
struct kernfs_node *kn;
- if (flags & LOOKUP_RCU)
+ if (flags & LOOKUP_RCU) {
+ kn = kernfs_dentry_node(dentry);
+ if (!kn) {
+ /* Negative hashed dentry, tell the VFS to switch to
+ * ref-walk mode and call us again so that node
+ * existence can be checked.
+ */
+ if (!d_unhashed(dentry))
+ return -ECHILD;
+
+ /* Negative unhashed dentry, this shouldn't happen
+ * because this case occurs in rcu-walk mode after
+ * dentry allocation which is followed by a call
+ * to ->loopup(). But if it does happen the dentry
+ * is surely invalid.
+ */
+ return 0;
+ }
+
+ /* Since the dentry is positive (we got the kernfs node) a
+ * kernfs node reference was held at the time. Now if the
+ * dentry reference count is still greater than 0 it's still
+ * positive so take a reference to the node to perform an
+ * active check.
+ */
+ if (d_count(dentry) <= 0 || !atomic_inc_not_zero(&kn->count))
+ return -ECHILD;
+
+ /* The kernfs node reference count was greater than 0, if
+ * it's active continue in rcu-walk mode.
+ */
+ if (kernfs_active_read(kn)) {
+ kernfs_put(kn);
+ return 1;
+ }
+
+ /* Otherwise, just tell the VFS to switch to ref-walk mode
+ * and call us again so the kernfs node can be validated.
+ */
+ kernfs_put(kn);
return -ECHILD;
+ }
- /* Always perform fresh lookup for negatives */
- if (d_really_is_negative(dentry))
- goto out_bad_unlocked;
+ down_read(&kernfs_rwsem);
kn = kernfs_dentry_node(dentry);
- down_read(&kernfs_rwsem);
+ if (!kn) {
+ struct kernfs_node *parent;
+
+ /* If the kernfs node can be found this is a stale negative
+ * hashed dentry so it must be discarded and the lookup redone.
+ */
+ parent = kernfs_dentry_node(dentry->d_parent);
+ if (parent) {
+ const void *ns = NULL;
+
+ if (kernfs_ns_enabled(parent))
+ ns = kernfs_info(dentry->d_parent->d_sb)->ns;
+ kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
+ if (kn)
+ goto out_bad;
+ }
+
+ /* The kernfs node doesn't exist, leave the dentry negative
+ * and return success.
+ */
+ goto out;
+ }
+
/* The kernfs node has been deactivated */
if (!kernfs_active_read(kn))
@@ -1072,12 +1132,11 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
if (kn->parent && kernfs_ns_enabled(kn->parent) &&
kernfs_info(dentry->d_sb)->ns != kn->ns)
goto out_bad;
-
+out:
up_read(&kernfs_rwsem);
return 1;
out_bad:
up_read(&kernfs_rwsem);
-out_bad_unlocked:
return 0;
}
@@ -1092,7 +1151,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
struct dentry *ret;
struct kernfs_node *parent = dir->i_private;
struct kernfs_node *kn;
- struct inode *inode;
+ struct inode *inode = NULL;
const void *ns = NULL;
down_read(&kernfs_rwsem);
@@ -1102,11 +1161,9 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
kn = kernfs_find_ns(parent, dentry->d_name.name, ns);
- /* no such entry */
- if (!kn || !kernfs_active(kn)) {
- ret = NULL;
- goto out_unlock;
- }
+ /* no such entry, retain as negative hashed dentry */
+ if (!kn || !kernfs_active(kn))
+ goto out_negative;
/* attach dentry and inode */
inode = kernfs_get_inode(dir->i_sb, kn);
@@ -1114,10 +1171,10 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
ret = ERR_PTR(-ENOMEM);
goto out_unlock;
}
-
+out_negative:
/* instantiate and hash dentry */
ret = d_splice_alias(inode, dentry);
- out_unlock:
+out_unlock:
up_read(&kernfs_rwsem);
return ret;
}
next prev parent reply other threads:[~2020-06-17 7:38 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-17 7:37 [PATCH v2 0/6] kernfs: proposed locking and concurrency improvement Ian Kent
2020-06-17 7:37 ` [PATCH v2 1/6] kernfs: switch kernfs to use an rwsem Ian Kent
2020-06-17 7:37 ` [PATCH v2 2/6] kernfs: move revalidate to be near lookup Ian Kent
2020-06-17 7:37 ` Ian Kent [this message]
2020-06-17 7:38 ` [PATCH v2 4/6] kernfs: use revision to identify directory node changes Ian Kent
2020-06-17 7:38 ` [PATCH v2 5/6] kernfs: refactor attr locking Ian Kent
2020-06-17 7:38 ` [PATCH v2 6/6] kernfs: make attr_mutex a local kernfs node lock Ian Kent
2020-06-19 15:38 ` [PATCH v2 0/6] kernfs: proposed locking and concurrency improvement Tejun Heo
2020-06-19 20:41 ` Rick Lindsley
2020-06-19 22:23 ` Tejun Heo
2020-06-20 2:44 ` Rick Lindsley
2020-06-22 17:53 ` Tejun Heo
2020-06-22 21:22 ` Rick Lindsley
2020-06-23 23:13 ` Tejun Heo
2020-06-24 9:04 ` Rick Lindsley
2020-06-24 9:27 ` Greg Kroah-Hartman
2020-06-24 13:19 ` Tejun Heo
2020-06-25 8:15 ` Ian Kent
2020-06-25 9:43 ` Greg Kroah-Hartman
2020-06-26 0:19 ` Ian Kent
2020-06-21 4:55 ` Ian Kent
2020-06-22 17:48 ` Tejun Heo
2020-06-22 18:03 ` Greg Kroah-Hartman
2020-06-22 21:27 ` Rick Lindsley
2020-06-23 5:21 ` Greg Kroah-Hartman
2020-06-23 5:09 ` Ian Kent
2020-06-23 6:02 ` Greg Kroah-Hartman
2020-06-23 8:01 ` Ian Kent
2020-06-23 8:29 ` Ian Kent
2020-06-23 11:49 ` Greg Kroah-Hartman
2020-06-23 9:33 ` Rick Lindsley
2020-06-23 11:45 ` Greg Kroah-Hartman
2020-06-23 22:55 ` Rick Lindsley
2020-06-23 11:51 ` Ian Kent
2020-06-21 3:21 ` Ian Kent
2020-12-10 16:44 ` Fox Chen
2020-12-11 2:01 ` [PATCH " Ian Kent
2020-12-11 2:17 ` Ian Kent
2020-12-13 3:46 ` Ian Kent
2020-12-14 6:14 ` Fox Chen
2020-12-14 13:30 ` Ian Kent
2020-12-15 8:33 ` Fox Chen
2020-12-15 12:59 ` Ian Kent
2020-12-17 4:46 ` Ian Kent
2020-12-17 8:54 ` Fox Chen
2020-12-17 10:09 ` Ian Kent
2020-12-17 11:09 ` Ian Kent
2020-12-17 11:48 ` Ian Kent
2020-12-17 15:14 ` Tejun Heo
2020-12-18 7:36 ` Ian Kent
2020-12-18 8:01 ` Fox Chen
2020-12-18 11:21 ` Ian Kent
2020-12-18 13:20 ` Fox Chen
2020-12-19 0:53 ` Ian Kent
2020-12-19 7:47 ` Fox Chen
2020-12-22 2:17 ` Ian Kent
2020-12-18 14:59 ` Tejun Heo
2020-12-19 7:08 ` Ian Kent
2020-12-19 16:23 ` Tejun Heo
2020-12-19 23:52 ` Ian Kent
2020-12-20 1:37 ` Ian Kent
2020-12-21 9:28 ` Fox Chen
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