[PATCH 44/46] fs: dcache per-bucket dcache hash locking

From: Nick Piggin
Date: Sat Nov 27 2010 - 05:30:13 EST

We can turn the dcache hash locking from a global dcache_hash_lock into
per-bucket locking.

Signed-off-by: Nick Piggin <npiggin@xxxxxxxxx>
---
fs/dcache.c | 131 ++++++++++++++++++++++++++++++++---------------
fs/super.c | 3 +-
include/linux/dcache.h | 23 ++-------
include/linux/fs.h | 3 +-
4 files changed, 97 insertions(+), 63 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 67a08d4..5e19940 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -33,13 +33,15 @@
#include <linux/bootmem.h>
#include <linux/fs_struct.h>
#include <linux/hardirq.h>
+#include <linux/bit_spinlock.h>
+#include <linux/rculist_bl.h>
#include "internal.h"

/*
* Usage:
* dcache_inode_lock protects:
* - i_dentry, d_alias, d_inode
- * dcache_hash_lock protects:
+ * dcache_hash_bucket lock protects:
* - the dcache hash table
* dcache_lru_lock protects:
* - the dcache lru lists and counters
@@ -57,7 +59,7 @@
* dcache_inode_lock
* dentry->d_lock
* dcache_lru_lock
- * dcache_hash_lock
+ * dcache_hash_bucket lock
*
* If there is an ancestor relationship:
* dentry->d_parent->...->d_parent->d_lock
@@ -74,13 +76,11 @@ int sysctl_vfs_cache_pressure __read_mostly = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);

__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_inode_lock);
-__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_hash_lock);
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);

EXPORT_SYMBOL(rename_lock);
EXPORT_SYMBOL(dcache_inode_lock);
-EXPORT_SYMBOL(dcache_hash_lock);

static struct kmem_cache *dentry_cache __read_mostly;

@@ -97,13 +97,35 @@ static struct kmem_cache *dentry_cache __read_mostly;

static unsigned int d_hash_mask __read_mostly;
static unsigned int d_hash_shift __read_mostly;
-static struct hlist_head *dentry_hashtable __read_mostly;
+
+struct dcache_hash_bucket {
+ struct hlist_bl_head head;
+};
+static struct dcache_hash_bucket *dentry_hashtable __read_mostly;

/* Statistics gathering. */
struct dentry_stat_t dentry_stat = {
.age_limit = 45,
};

+static inline struct dcache_hash_bucket *d_hash(struct dentry *parent,
+ unsigned long hash)
+{
+ hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
+ hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
+ return dentry_hashtable + (hash & D_HASHMASK);
+}
+
+static inline void spin_lock_bucket(struct dcache_hash_bucket *b)
+{
+ bit_spin_lock(0, (unsigned long *)b);
+}
+
+static inline void spin_unlock_bucket(struct dcache_hash_bucket *b)
+{
+ __bit_spin_unlock(0, (unsigned long *)b);
+}
+
static struct percpu_counter nr_dentry __cacheline_aligned_in_smp;
static struct percpu_counter nr_dentry_unused __cacheline_aligned_in_smp;

@@ -138,7 +160,7 @@ static void d_free(struct dentry *dentry)
dentry->d_op->d_release(dentry);

/* if dentry was never inserted into hash, immediate free is OK */
- if (hlist_unhashed(&dentry->d_hash))
+ if (hlist_bl_unhashed(&dentry->d_hash))
__d_free(&dentry->d_u.d_rcu);
else
call_rcu(&dentry->d_u.d_rcu, __d_free);
@@ -278,6 +300,39 @@ relock:
return d_kill(dentry, parent);
}

+void __d_drop(struct dentry *dentry)
+{
+ if (!(dentry->d_flags & DCACHE_UNHASHED)) {
+ if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED)) {
+ bit_spin_lock(0, (unsigned long *)&dentry->d_sb->s_anon);
+ dentry->d_flags |= DCACHE_UNHASHED;
+ hlist_bl_del_init(&dentry->d_hash);
+ __bit_spin_unlock(0, (unsigned long *)&dentry->d_sb->s_anon);
+ } else {
+ struct dcache_hash_bucket *b;
+ b = d_hash(dentry->d_parent, dentry->d_name.hash);
+ spin_lock_bucket(b);
+ /*
+ * We may not actually need to put DCACHE_UNHASHED
+ * manipulations under the hash lock, but follow
+ * the principle of least surprise.
+ */
+ dentry->d_flags |= DCACHE_UNHASHED;
+ hlist_bl_del_rcu(&dentry->d_hash);
+ spin_unlock_bucket(b);
+ }
+ }
+}
+EXPORT_SYMBOL(__d_drop);
+
+void d_drop(struct dentry *dentry)
+{
+ spin_lock(&dentry->d_lock);
+ __d_drop(dentry);
+ spin_unlock(&dentry->d_lock);
+}
+EXPORT_SYMBOL(d_drop);
+
/*
* This is dput
*
@@ -891,8 +946,8 @@ void shrink_dcache_for_umount(struct super_block *sb)
spin_unlock(&dentry->d_lock);
shrink_dcache_for_umount_subtree(dentry);

- while (!hlist_empty(&sb->s_anon)) {
- dentry = hlist_entry(sb->s_anon.first, struct dentry, d_hash);
+ while (!hlist_bl_empty(&sb->s_anon)) {
+ dentry = hlist_bl_entry(hlist_bl_first(&sb->s_anon), struct dentry, d_hash);
shrink_dcache_for_umount_subtree(dentry);
}
}
@@ -1196,7 +1251,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
dentry->d_sb = NULL;
dentry->d_op = NULL;
dentry->d_fsdata = NULL;
- INIT_HLIST_NODE(&dentry->d_hash);
+ INIT_HLIST_BL_NODE(&dentry->d_hash);
INIT_LIST_HEAD(&dentry->d_lru);
INIT_LIST_HEAD(&dentry->d_subdirs);
INIT_LIST_HEAD(&dentry->d_alias);
@@ -1387,14 +1442,6 @@ struct dentry * d_alloc_root(struct inode * root_inode)
}
EXPORT_SYMBOL(d_alloc_root);

-static inline struct hlist_head *d_hash(struct dentry *parent,
- unsigned long hash)
-{
- hash += ((unsigned long) parent ^ GOLDEN_RATIO_PRIME) / L1_CACHE_BYTES;
- hash = hash ^ ((hash ^ GOLDEN_RATIO_PRIME) >> D_HASHBITS);
- return dentry_hashtable + (hash & D_HASHMASK);
-}
-
/**
* d_obtain_alias - find or allocate a dentry for a given inode
* @inode: inode to allocate the dentry for
@@ -1449,11 +1496,11 @@ struct dentry *d_obtain_alias(struct inode *inode)
tmp->d_sb = inode->i_sb;
tmp->d_inode = inode;
tmp->d_flags |= DCACHE_DISCONNECTED;
- tmp->d_flags &= ~DCACHE_UNHASHED;
list_add(&tmp->d_alias, &inode->i_dentry);
- spin_lock(&dcache_hash_lock);
- hlist_add_head(&tmp->d_hash, &inode->i_sb->s_anon);
- spin_unlock(&dcache_hash_lock);
+ bit_spin_lock(0, (unsigned long *)&tmp->d_sb->s_anon);
+ tmp->d_flags &= ~DCACHE_UNHASHED;
+ hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
+ __bit_spin_unlock(0, (unsigned long *)&tmp->d_sb->s_anon);
spin_unlock(&tmp->d_lock);
spin_unlock(&dcache_inode_lock);

@@ -1617,8 +1664,8 @@ struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
unsigned int len = name->len;
unsigned int hash = name->hash;
const unsigned char *str = name->name;
- struct hlist_head *head = d_hash(parent,hash);
- struct hlist_node *node;
+ struct dcache_hash_bucket *b = d_hash(parent, hash);
+ struct hlist_bl_node *node;
struct dentry *dentry;

/*
@@ -1641,7 +1688,7 @@ struct dentry *__d_lookup_rcu(struct dentry *parent, struct qstr *name,
*
* See Documentation/vfs/dcache-locking.txt for more details.
*/
- hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
+ hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
struct inode *i;
const char *tname;
int tlen;
@@ -1754,8 +1801,8 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
unsigned int len = name->len;
unsigned int hash = name->hash;
const unsigned char *str = name->name;
- struct hlist_head *head = d_hash(parent,hash);
- struct hlist_node *node;
+ struct dcache_hash_bucket *b = d_hash(parent, hash);
+ struct hlist_bl_node *node;
struct dentry *found = NULL;
struct dentry *dentry;

@@ -1781,7 +1828,7 @@ struct dentry *__d_lookup(struct dentry *parent, struct qstr *name)
*/
rcu_read_lock();

- hlist_for_each_entry_rcu(dentry, node, head, d_hash) {
+ hlist_bl_for_each_entry_rcu(dentry, node, &b->head, d_hash) {
const char *tname;
int tlen;

@@ -1932,11 +1979,12 @@ again:
}
EXPORT_SYMBOL(d_delete);

-static void __d_rehash(struct dentry * entry, struct hlist_head *list)
+static void __d_rehash(struct dentry * entry, struct dcache_hash_bucket *b)
{
-
+ spin_lock_bucket(b);
entry->d_flags &= ~DCACHE_UNHASHED;
- hlist_add_head_rcu(&entry->d_hash, list);
+ hlist_bl_add_head_rcu(&entry->d_hash, &b->head);
+ spin_unlock_bucket(b);
}

static void _d_rehash(struct dentry * entry)
@@ -1954,9 +2002,7 @@ static void _d_rehash(struct dentry * entry)
void d_rehash(struct dentry * entry)
{
spin_lock(&entry->d_lock);
- spin_lock(&dcache_hash_lock);
_d_rehash(entry);
- spin_unlock(&dcache_hash_lock);
spin_unlock(&entry->d_lock);
}
EXPORT_SYMBOL(d_rehash);
@@ -2035,6 +2081,7 @@ static void switch_names(struct dentry *dentry, struct dentry *target)
*/
void d_move(struct dentry * dentry, struct dentry * target)
{
+ struct dcache_hash_bucket *b;
if (!dentry->d_inode)
printk(KERN_WARNING "VFS: moving negative dcache entry\n");

@@ -2065,11 +2112,13 @@ void d_move(struct dentry * dentry, struct dentry * target)
}

/* Move the dentry to the target hash queue, if on different bucket */
- spin_lock(&dcache_hash_lock);
- if (!d_unhashed(dentry))
- hlist_del_rcu(&dentry->d_hash);
+ if (!d_unhashed(dentry)) {
+ b = d_hash(dentry->d_parent, dentry->d_name.hash);
+ spin_lock_bucket(b);
+ hlist_bl_del_rcu(&dentry->d_hash);
+ spin_unlock_bucket(b);
+ }
__d_rehash(dentry, d_hash(target->d_parent, target->d_name.hash));
- spin_unlock(&dcache_hash_lock);

/* Unhash the target: dput() will then get rid of it */
__d_drop(target);
@@ -2280,9 +2329,7 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode)

spin_lock(&actual->d_lock);
found:
- spin_lock(&dcache_hash_lock);
_d_rehash(actual);
- spin_unlock(&dcache_hash_lock);
spin_unlock(&actual->d_lock);
spin_unlock(&dcache_inode_lock);
out_nolock:
@@ -2864,7 +2911,7 @@ static void __init dcache_init_early(void)

dentry_hashtable =
alloc_large_system_hash("Dentry cache",
- sizeof(struct hlist_head),
+ sizeof(struct dcache_hash_bucket),
dhash_entries,
13,
HASH_EARLY,
@@ -2873,7 +2920,7 @@ static void __init dcache_init_early(void)
0);

for (loop = 0; loop < (1 << d_hash_shift); loop++)
- INIT_HLIST_HEAD(&dentry_hashtable[loop]);
+ INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
}

static void __init dcache_init(void)
@@ -2899,7 +2946,7 @@ static void __init dcache_init(void)

dentry_hashtable =
alloc_large_system_hash("Dentry cache",
- sizeof(struct hlist_head),
+ sizeof(struct dcache_hash_bucket),
dhash_entries,
13,
0,
@@ -2908,7 +2955,7 @@ static void __init dcache_init(void)
0);

for (loop = 0; loop < (1 << d_hash_shift); loop++)
- INIT_HLIST_HEAD(&dentry_hashtable[loop]);
+ INIT_HLIST_BL_HEAD(&dentry_hashtable[loop].head);
}

/* SLAB cache for __getname() consumers */
diff --git a/fs/super.c b/fs/super.c
index ca69615..968ba01 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -30,6 +30,7 @@
#include <linux/idr.h>
#include <linux/mutex.h>
#include <linux/backing-dev.h>
+#include <linux/rculist_bl.h>
#include "internal.h"


@@ -71,7 +72,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
INIT_LIST_HEAD(&s->s_files);
#endif
INIT_LIST_HEAD(&s->s_instances);
- INIT_HLIST_HEAD(&s->s_anon);
+ INIT_HLIST_BL_HEAD(&s->s_anon);
INIT_LIST_HEAD(&s->s_inodes);
INIT_LIST_HEAD(&s->s_dentry_lru);
init_rwsem(&s->s_umount);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 72f5f32..97c2d78 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -4,6 +4,7 @@
#include <asm/atomic.h>
#include <linux/list.h>
#include <linux/rculist.h>
+#include <linux/rculist_bl.h>
#include <linux/spinlock.h>
#include <linux/seqlock.h>
#include <linux/cache.h>
@@ -91,7 +92,7 @@ struct dentry {
/* RCU lookup touched fields */
unsigned int d_flags; /* protected by d_lock */
seqcount_t d_seq; /* per dentry seqlock */
- struct hlist_node d_hash; /* lookup hash list */
+ struct hlist_bl_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
struct inode *d_inode; /* Where the name belongs to - NULL is
@@ -193,7 +194,6 @@ struct dentry_operations {
(DCACHE_OP_REVALIDATE|DCACHE_OP_REVALIDATE_RCU)

extern spinlock_t dcache_inode_lock;
-extern spinlock_t dcache_hash_lock;
extern seqlock_t rename_lock;

/**
@@ -211,23 +211,8 @@ extern seqlock_t rename_lock;
*
* __d_drop requires dentry->d_lock.
*/
-
-static inline void __d_drop(struct dentry *dentry)
-{
- if (!(dentry->d_flags & DCACHE_UNHASHED)) {
- dentry->d_flags |= DCACHE_UNHASHED;
- spin_lock(&dcache_hash_lock);
- hlist_del_rcu(&dentry->d_hash);
- spin_unlock(&dcache_hash_lock);
- }
-}
-
-static inline void d_drop(struct dentry *dentry)
-{
- spin_lock(&dentry->d_lock);
- __d_drop(dentry);
- spin_unlock(&dentry->d_lock);
-}
+void d_drop(struct dentry *dentry);
+void __d_drop(struct dentry *dentry);

static inline int dname_external(struct dentry *dentry)
{
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 490eedd..315d0e9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -392,6 +392,7 @@ struct inodes_stat_t {
#include <linux/capability.h>
#include <linux/semaphore.h>
#include <linux/fiemap.h>
+#include <linux/rculist_bl.h>

#include <asm/atomic.h>
#include <asm/byteorder.h>
@@ -1376,7 +1377,7 @@ struct super_block {
const struct xattr_handler **s_xattr;

struct list_head s_inodes; /* all inodes */
- struct hlist_head s_anon; /* anonymous dentries for (nfs) exporting */
+ struct hlist_bl_head s_anon; /* anonymous dentries for (nfs) exporting */
#ifdef CONFIG_SMP
struct list_head __percpu *s_files;
#else
--
1.7.1

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