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Subject[patch 08/27] fs: dcache scale lru
Add a new lock, dcache_lru_lock, to protect the dcache hash table from
concurrent modification. d_lru is also protected by d_lock.

Move lru scanning out from underneath dcache_lock.

---
fs/dcache.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 85 insertions(+), 20 deletions(-)
Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -36,17 +36,26 @@

/*
* Usage:
- * dcache_hash_lock protects dcache hash table
+ * dcache_hash_lock protects:
+ * - the dcache hash table
+ * dcache_lru_lock protects:
+ * - the dcache lru lists and counters
+ * d_lock protects:
+ * - d_flags
+ * - d_name
+ * - d_lru
*
* Ordering:
* dcache_lock
* dentry->d_lock
+ * dcache_lru_lock
* dcache_hash_lock
*/
int sysctl_vfs_cache_pressure __read_mostly = 100;
EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure);

__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_hash_lock);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lru_lock);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(dcache_lock);
__cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock);

@@ -133,37 +142,56 @@ static void dentry_iput(struct dentry *
}

/*
- * dentry_lru_(add|add_tail|del|del_init) must be called with dcache_lock held.
+ * dentry_lru_(add|add_tail|del|del_init) must be called with d_lock held
+ * to protect list_empty(d_lru) condition.
*/
static void dentry_lru_add(struct dentry *dentry)
{
+ spin_lock(&dcache_lru_lock);
list_add(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
dentry->d_sb->s_nr_dentry_unused++;
dentry_stat.nr_unused++;
+ spin_unlock(&dcache_lru_lock);
}

static void dentry_lru_add_tail(struct dentry *dentry)
{
+ spin_lock(&dcache_lru_lock);
list_add_tail(&dentry->d_lru, &dentry->d_sb->s_dentry_lru);
dentry->d_sb->s_nr_dentry_unused++;
dentry_stat.nr_unused++;
+ spin_unlock(&dcache_lru_lock);
+}
+
+static void __dentry_lru_del(struct dentry *dentry)
+{
+ list_del(&dentry->d_lru);
+ dentry->d_sb->s_nr_dentry_unused--;
+ dentry_stat.nr_unused--;
+}
+
+static void __dentry_lru_del_init(struct dentry *dentry)
+{
+ list_del_init(&dentry->d_lru);
+ dentry->d_sb->s_nr_dentry_unused--;
+ dentry_stat.nr_unused--;
}

static void dentry_lru_del(struct dentry *dentry)
{
if (!list_empty(&dentry->d_lru)) {
- list_del(&dentry->d_lru);
- dentry->d_sb->s_nr_dentry_unused--;
- dentry_stat.nr_unused--;
+ spin_lock(&dcache_lru_lock);
+ __dentry_lru_del(dentry);
+ spin_unlock(&dcache_lru_lock);
}
}

static void dentry_lru_del_init(struct dentry *dentry)
{
if (likely(!list_empty(&dentry->d_lru))) {
- list_del_init(&dentry->d_lru);
- dentry->d_sb->s_nr_dentry_unused--;
- dentry_stat.nr_unused--;
+ spin_lock(&dcache_lru_lock);
+ __dentry_lru_del_init(dentry);
+ spin_unlock(&dcache_lru_lock);
}
}

@@ -174,6 +202,8 @@ static void dentry_lru_del_init(struct d
* The dentry must already be unhashed and removed from the LRU.
*
* If this is the root of the dentry tree, return NULL.
+ *
+ * dcache_lock and d_lock must be held by caller, are dropped by d_kill.
*/
static struct dentry *d_kill(struct dentry *dentry)
__releases(dentry->d_lock)
@@ -326,11 +356,19 @@ int d_invalidate(struct dentry * dentry)
}

/* This should be called _only_ with dcache_lock held */
+static inline struct dentry * __dget_locked_dlock(struct dentry *dentry)
+{
+ atomic_inc(&dentry->d_count);
+ dentry_lru_del_init(dentry);
+ return dentry;
+}

static inline struct dentry * __dget_locked(struct dentry *dentry)
{
atomic_inc(&dentry->d_count);
+ spin_lock(&dentry->d_lock);
dentry_lru_del_init(dentry);
+ spin_lock(&dentry->d_lock);
return dentry;
}

@@ -407,7 +445,7 @@ restart:
list_for_each_entry(dentry, &inode->i_dentry, d_alias) {
spin_lock(&dentry->d_lock);
if (!atomic_read(&dentry->d_count)) {
- __dget_locked(dentry);
+ __dget_locked_dlock(dentry);
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
spin_unlock(&dcache_lock);
@@ -439,17 +477,18 @@ static void prune_one_dentry(struct dent
* Prune ancestors. Locking is simpler than in dput(),
* because dcache_lock needs to be taken anyway.
*/
- spin_lock(&dcache_lock);
while (dentry) {
- if (!atomic_dec_and_lock(&dentry->d_count, &dentry->d_lock))
+ spin_lock(&dcache_lock);
+ if (!atomic_dec_and_lock(&dentry->d_count, &dentry->d_lock)) {
+ spin_unlock(&dcache_lock);
return;
+ }

if (dentry->d_op && dentry->d_op->d_delete)
dentry->d_op->d_delete(dentry);
dentry_lru_del_init(dentry);
__d_drop(dentry);
dentry = d_kill(dentry);
- spin_lock(&dcache_lock);
}
}

@@ -470,10 +509,11 @@ static void __shrink_dcache_sb(struct su

BUG_ON(!sb);
BUG_ON((flags & DCACHE_REFERENCED) && count == NULL);
- spin_lock(&dcache_lock);
if (count != NULL)
/* called from prune_dcache() and shrink_dcache_parent() */
cnt = *count;
+relock:
+ spin_lock(&dcache_lru_lock);
restart:
if (count == NULL)
list_splice_init(&sb->s_dentry_lru, &tmp);
@@ -483,7 +523,10 @@ restart:
struct dentry, d_lru);
BUG_ON(dentry->d_sb != sb);

- spin_lock(&dentry->d_lock);
+ if (!spin_trylock(&dentry->d_lock)) {
+ spin_unlock(&dcache_lru_lock);
+ goto relock;
+ }
/*
* If we are honouring the DCACHE_REFERENCED flag and
* the dentry has this flag set, don't free it. Clear
@@ -501,13 +544,22 @@ restart:
if (!cnt)
break;
}
- cond_resched_lock(&dcache_lock);
+ cond_resched_lock(&dcache_lru_lock);
}
}
+ spin_unlock(&dcache_lru_lock);
+
+ spin_lock(&dcache_lock);
+again:
+ spin_lock(&dcache_lru_lock); /* lru_lock also protects tmp list */
while (!list_empty(&tmp)) {
dentry = list_entry(tmp.prev, struct dentry, d_lru);
- dentry_lru_del_init(dentry);
- spin_lock(&dentry->d_lock);
+
+ if (!spin_trylock(&dentry->d_lock)) {
+ spin_unlock(&dcache_lru_lock);
+ goto again;
+ }
+ __dentry_lru_del_init(dentry);
/*
* We found an inuse dentry which was not removed from
* the LRU because of laziness during lookup. Do not free
@@ -517,17 +569,22 @@ restart:
spin_unlock(&dentry->d_lock);
continue;
}
+
+ spin_unlock(&dcache_lru_lock);
prune_one_dentry(dentry);
- /* dentry->d_lock was dropped in prune_one_dentry() */
- cond_resched_lock(&dcache_lock);
+ /* dcache_lock and dentry->d_lock dropped */
+ spin_lock(&dcache_lock);
+ spin_lock(&dcache_lru_lock);
}
+ spin_unlock(&dcache_lock);
+
if (count == NULL && !list_empty(&sb->s_dentry_lru))
goto restart;
if (count != NULL)
*count = cnt;
if (!list_empty(&referenced))
list_splice(&referenced, &sb->s_dentry_lru);
- spin_unlock(&dcache_lock);
+ spin_unlock(&dcache_lru_lock);
}

/**
@@ -635,7 +692,9 @@ static void shrink_dcache_for_umount_sub

/* detach this root from the system */
spin_lock(&dcache_lock);
+ spin_lock(&dentry->d_lock);
dentry_lru_del_init(dentry);
+ spin_unlock(&dentry->d_lock);
__d_drop(dentry);
spin_unlock(&dcache_lock);

@@ -649,7 +708,9 @@ static void shrink_dcache_for_umount_sub
spin_lock(&dcache_lock);
list_for_each_entry(loop, &dentry->d_subdirs,
d_u.d_child) {
+ spin_lock(&loop->d_lock);
dentry_lru_del_init(loop);
+ spin_unlock(&loop->d_lock);
__d_drop(loop);
cond_resched_lock(&dcache_lock);
}
@@ -832,13 +893,17 @@ resume:
struct dentry *dentry = list_entry(tmp, struct dentry, d_u.d_child);
next = tmp->next;

+ spin_lock(&dentry->d_lock);
dentry_lru_del_init(dentry);
+ spin_unlock(&dentry->d_lock);
/*
* move only zero ref count dentries to the end
* of the unused list for prune_dcache
*/
if (!atomic_read(&dentry->d_count)) {
+ spin_lock(&dentry->d_lock);
dentry_lru_add_tail(dentry);
+ spin_unlock(&dentry->d_lock);
found++;
}




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