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Subject[PATCH 28/46] fs: use RCU in shrink_dentry_list to reduce lock nesting
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
---
fs/dcache.c | 38 +++++++++++++++++++++-----------------
1 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index 5a7c328..4dbcb6c 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -580,16 +580,16 @@ static void shrink_dentry_list(struct list_head *list)
{
struct dentry *dentry;

+ rcu_read_lock();
while (!list_empty(list)) {
struct dentry *parent;

dentry = list_entry(list->prev, struct dentry, d_lru);

- if (!spin_trylock(&dentry->d_lock)) {
-relock1:
- spin_unlock(&dcache_lru_lock);
- cpu_relax();
- spin_lock(&dcache_lru_lock);
+ /* Don't need RCU dereference because we recheck under lock */
+ spin_lock(&dentry->d_lock);
+ if (dentry != list_entry(list->prev, struct dentry, d_lru)) {
+ spin_unlock(&dentry->d_lock);
continue;
}

@@ -599,14 +599,16 @@ relock1:
* it - just keep it off the LRU list.
*/
if (dentry->d_count) {
- __dentry_lru_del(dentry);
+ dentry_lru_del(dentry);
spin_unlock(&dentry->d_lock);
continue;
}
+
if (!spin_trylock(&dcache_inode_lock)) {
-relock2:
+relock:
spin_unlock(&dentry->d_lock);
- goto relock1;
+ cpu_relax();
+ continue;
}
if (IS_ROOT(dentry))
parent = NULL;
@@ -614,15 +616,15 @@ relock2:
parent = dentry->d_parent;
if (parent && !spin_trylock(&parent->d_lock)) {
spin_unlock(&dcache_inode_lock);
- goto relock2;
+ goto relock;
}
- __dentry_lru_del(dentry);
- spin_unlock(&dcache_lru_lock);
+ dentry_lru_del(dentry);

+ rcu_read_unlock();
prune_one_dentry(dentry, parent);
- /* dcache_inode_lock and dentry->d_lock dropped */
- spin_lock(&dcache_lru_lock);
+ rcu_read_lock();
}
+ rcu_read_unlock();
}

/**
@@ -671,13 +673,13 @@ relock:
break;
}
}
-
- *count = cnt;
- shrink_dentry_list(&tmp);
-
if (!list_empty(&referenced))
list_splice(&referenced, &sb->s_dentry_lru);
spin_unlock(&dcache_lru_lock);
+
+ shrink_dentry_list(&tmp);
+
+ *count = cnt;
}

/**
@@ -769,7 +771,9 @@ void shrink_dcache_sb(struct super_block *sb)
spin_lock(&dcache_lru_lock);
while (!list_empty(&sb->s_dentry_lru)) {
list_splice_init(&sb->s_dentry_lru, &tmp);
+ spin_unlock(&dcache_lru_lock);
shrink_dentry_list(&tmp);
+ spin_lock(&dcache_lru_lock);
}
spin_unlock(&dcache_lru_lock);
}
--
1.7.1


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