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Date: Fri, 28 Oct 2011 10:02:42 -0700 (PDT)
From: Sage Weil <sage@...dream.net>
To: Christoph Hellwig <hch@...radead.org>
cc: Dave Chinner <david@...morbit.com>, linux-fsdevel@...r.kernel.org,
viro@...IV.linux.org.uk, ceph-devel@...r.kernel.org,
rwheeler@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] vfs: add d_prune dentry operation
On Fri, 28 Oct 2011, Christoph Hellwig wrote:
> This variant seems to crash btrfs in xfstests 010:
This got rebased enough times that DCACHE_OP_PRUNE collided with
DCACHE_NEEDS_LOOKUP. The version below fixes that, and also renumbers a
few of those constants to group it with the other DCACHE_OP_* guys. I
assume it's okay to switch those up?
sage
>From 2c39148ba12ce13442d66319f9d1ba91ce62974d Mon Sep 17 00:00:00 2001
From: Sage Weil <sage@...dream.net>
Date: Fri, 28 Oct 2011 09:55:21 -0700
Subject: [PATCH] vfs: add d_prune dentry operation
This adds a d_prune dentry operation that is called by the VFS prior to
pruning (i.e. unhashing and killing) a hashed dentry from the dcache.
Wrap dentry_lru_del() and use the new _prune() helper in the cases where we
are about to unhash and kill the dentry.
This will be used by Ceph to maintain a flag indicating whether the
complete contents of a directory are contained in the dcache, allowing it
to satisfy lookups and readdir without addition server communication.
Renumber a few DCACHE_* #defines to group DCACHE_OP_PRUNE with the other
DCACHE_OP_ bits.
Signed-off-by: Sage Weil <sage@...dream.net>
---
v4: fixed DCACHE_OP_PRUNE collision with DCACHE_NEEDS_LOOKUP.
v3: better comments for dentry_lru_{del,prune}
v2: move prune call into dentry_lru_prune() wrapper
Documentation/filesystems/Locking | 1 +
fs/dcache.c | 40 ++++++++++++++++++++++++++++++++----
include/linux/dcache.h | 8 ++++--
3 files changed, 41 insertions(+), 8 deletions(-)
diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 6533807..d819ba1 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -29,6 +29,7 @@ d_hash no no no maybe
d_compare: yes no no maybe
d_delete: no yes no no
d_release: no no yes no
+d_prune: no yes no no
d_iput: no no yes no
d_dname: no no no no
d_automount: no no yes no
diff --git a/fs/dcache.c b/fs/dcache.c
index a88948b..274f13e 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -225,7 +225,7 @@ static void dentry_unlink_inode(struct dentry * dentry)
}
/*
- * dentry_lru_(add|del|move_tail) must be called with d_lock held.
+ * dentry_lru_(add|del|prune|move_tail) must be called with d_lock held.
*/
static void dentry_lru_add(struct dentry *dentry)
{
@@ -245,6 +245,9 @@ static void __dentry_lru_del(struct dentry *dentry)
dentry_stat.nr_unused--;
}
+/*
+ * Remove a dentry with references from the LRU.
+ */
static void dentry_lru_del(struct dentry *dentry)
{
if (!list_empty(&dentry->d_lru)) {
@@ -254,6 +257,23 @@ static void dentry_lru_del(struct dentry *dentry)
}
}
+/*
+ * Remove a dentry that is unreferenced and about to be pruned
+ * (unhashed and destroyed) from the LRU, and inform the file system.
+ * This wrapper should be called _prior_ to unhashing a victim dentry.
+ */
+static void dentry_lru_prune(struct dentry *dentry)
+{
+ if (!list_empty(&dentry->d_lru)) {
+ if (dentry->d_flags & DCACHE_OP_PRUNE)
+ dentry->d_op->d_prune(dentry);
+
+ spin_lock(&dcache_lru_lock);
+ __dentry_lru_del(dentry);
+ spin_unlock(&dcache_lru_lock);
+ }
+}
+
static void dentry_lru_move_tail(struct dentry *dentry)
{
spin_lock(&dcache_lru_lock);
@@ -403,8 +423,12 @@ relock:
if (ref)
dentry->d_count--;
- /* if dentry was on the d_lru list delete it from there */
- dentry_lru_del(dentry);
+ /*
+ * if dentry was on the d_lru list delete it from there.
+ * inform the fs via d_prune that this dentry is about to be
+ * unhashed and destroyed.
+ */
+ dentry_lru_prune(dentry);
/* if it was on the hash then remove it */
__d_drop(dentry);
return d_kill(dentry, parent);
@@ -854,8 +878,12 @@ static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
do {
struct inode *inode;
- /* detach from the system */
- dentry_lru_del(dentry);
+ /*
+ * remove the dentry from the lru, and inform
+ * the fs that this dentry is about to be
+ * unhashed and destroyed.
+ */
+ dentry_lru_prune(dentry);
__d_shrink(dentry);
if (dentry->d_count != 0) {
@@ -1283,6 +1311,8 @@ void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op)
dentry->d_flags |= DCACHE_OP_REVALIDATE;
if (op->d_delete)
dentry->d_flags |= DCACHE_OP_DELETE;
+ if (op->d_prune)
+ dentry->d_flags |= DCACHE_OP_PRUNE;
}
EXPORT_SYMBOL(d_set_d_op);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 62157c0..4df9261 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -165,6 +165,7 @@ struct dentry_operations {
unsigned int, const char *, const struct qstr *);
int (*d_delete)(const struct dentry *);
void (*d_release)(struct dentry *);
+ void (*d_prune)(struct dentry *);
void (*d_iput)(struct dentry *, struct inode *);
char *(*d_dname)(struct dentry *, char *, int);
struct vfsmount *(*d_automount)(struct path *);
@@ -184,8 +185,9 @@ struct dentry_operations {
#define DCACHE_OP_COMPARE 0x0002
#define DCACHE_OP_REVALIDATE 0x0004
#define DCACHE_OP_DELETE 0x0008
+#define DCACHE_OP_PRUNE 0x0010
-#define DCACHE_DISCONNECTED 0x0010
+#define DCACHE_DISCONNECTED 0x0020
/* This dentry is possibly not currently connected to the dcache tree, in
* which case its parent will either be itself, or will have this flag as
* well. nfsd will not use a dentry with this bit set, but will first
@@ -196,8 +198,8 @@ struct dentry_operations {
* dentry into place and return that dentry rather than the passed one,
* typically using d_splice_alias. */
-#define DCACHE_REFERENCED 0x0020 /* Recently used, don't discard. */
-#define DCACHE_RCUACCESS 0x0040 /* Entry has ever been RCU-visible */
+#define DCACHE_REFERENCED 0x0040 /* Recently used, don't discard. */
+#define DCACHE_RCUACCESS 0x0080 /* Entry has ever been RCU-visible */
#define DCACHE_CANT_MOUNT 0x0100
#define DCACHE_GENOCIDE 0x0200
--
1.7.0
--
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