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Date: Wed, 27 Oct 2010 15:23:03 +1100
From: Dave Chinner <david@...morbit.com>
To: viro@...IV.linux.org.uk
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/4] fs: Lock the inode LRU list separately
From: Dave Chinner <dchinner@...hat.com>
Introduce the inode_lru_lock to protect the inode_lru list. This
lock is nested inside the inode->i_lock to allow the inode to be
added to the LRU list in iput_final without needing to deal with
lock inversions. This keeps iput_final() clean and neat.
Further, where marking the inode I_FREEING and removing it from the
LRU, move the LRU list manipulation within the inode->i_lock to keep
the list manipulation consistent with iput_final. This also means
that most of the open coded LRU list removal + unused inode
accounting can now use the inode_lru_list_del() wrappers which
cleans the code up further.
However, this locking change means what the LRU traversal in
prune_icache() inverts this lock ordering and needs to use trylock
semantics on the inode->i_lock to avoid deadlocking. In these cases,
if we fail to lock the inode we move it to the back of the LRU to
prevent spinning on it.
Signed-off-by: Dave Chinner <dchinner@...hat.com>
---
fs/inode.c | 45 +++++++++++++++++++++++++++++----------------
1 files changed, 29 insertions(+), 16 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index f134aa4..e04371e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -30,10 +30,13 @@
*
* inode->i_lock protects:
* i_state
+ * inode_lru_lock protects:
+ * inode_lru, i_lru
*
* Lock ordering:
* inode_lock
* inode->i_lock
+ * inode_lru_lock
*/
/*
@@ -83,6 +86,7 @@ static unsigned int i_hash_shift __read_mostly;
*/
static LIST_HEAD(inode_lru);
+static DEFINE_SPINLOCK(inode_lru_lock);
static struct hlist_head *inode_hashtable __read_mostly;
/*
@@ -344,16 +348,20 @@ EXPORT_SYMBOL(ihold);
static void inode_lru_list_add(struct inode *inode)
{
if (list_empty(&inode->i_lru)) {
+ spin_lock(&inode_lru_lock);
list_add(&inode->i_lru, &inode_lru);
percpu_counter_inc(&nr_inodes_unused);
+ spin_unlock(&inode_lru_lock);
}
}
static void inode_lru_list_del(struct inode *inode)
{
if (!list_empty(&inode->i_lru)) {
+ spin_lock(&inode_lru_lock);
list_del_init(&inode->i_lru);
percpu_counter_dec(&nr_inodes_unused);
+ spin_unlock(&inode_lru_lock);
}
}
@@ -537,15 +545,10 @@ void evict_inodes(struct super_block *sb)
}
inode->i_state |= I_FREEING;
- if (!(inode->i_state & (I_DIRTY | I_SYNC)))
- percpu_counter_dec(&nr_inodes_unused);
+ inode_lru_list_del(inode);
spin_unlock(&inode->i_lock);
- /*
- * Move the inode off the IO lists and LRU once I_FREEING is
- * set so that it won't get moved back on there if it is dirty.
- */
- list_move(&inode->i_lru, &dispose);
+ list_add(&inode->i_lru, &dispose);
}
spin_unlock(&inode_lock);
@@ -582,15 +585,10 @@ int invalidate_inodes(struct super_block *sb)
}
inode->i_state |= I_FREEING;
- if (!(inode->i_state & (I_DIRTY | I_SYNC)))
- percpu_counter_dec(&nr_inodes_unused);
+ inode_lru_list_del(inode);
spin_unlock(&inode->i_lock);
- /*
- * Move the inode off the IO lists and LRU once I_FREEING is
- * set so that it won't get moved back on there if it is dirty.
- */
- list_move(&inode->i_lru, &dispose);
+ list_add(&inode->i_lru, &dispose);
}
spin_unlock(&inode_lock);
@@ -637,6 +635,7 @@ static void prune_icache(int nr_to_scan)
down_read(&iprune_sem);
spin_lock(&inode_lock);
+ spin_lock(&inode_lru_lock);
for (nr_scanned = 0; nr_scanned < nr_to_scan; nr_scanned++) {
struct inode *inode;
@@ -646,10 +645,19 @@ static void prune_icache(int nr_to_scan)
inode = list_entry(inode_lru.prev, struct inode, i_lru);
/*
+ * we are inverting the inode_lru_lock/inode->i_lock here,
+ * so use a trylock. If we fail to get the lock, just move the
+ * inode to the back of the list so we don't spin on it.
+ */
+ if (!spin_trylock(&inode->i_lock)) {
+ list_move(&inode->i_lru, &inode_lru);
+ continue;
+ }
+
+ /*
* Referenced or dirty inodes are still in use. Give them
* another pass through the LRU as we canot reclaim them now.
*/
- spin_lock(&inode->i_lock);
if (atomic_read(&inode->i_count) ||
(inode->i_state & ~I_REFERENCED)) {
spin_unlock(&inode->i_lock);
@@ -668,17 +676,21 @@ static void prune_icache(int nr_to_scan)
if (inode_has_buffers(inode) || inode->i_data.nrpages) {
__iget(inode);
spin_unlock(&inode->i_lock);
+ spin_unlock(&inode_lru_lock);
spin_unlock(&inode_lock);
if (remove_inode_buffers(inode))
reap += invalidate_mapping_pages(&inode->i_data,
0, -1);
iput(inode);
spin_lock(&inode_lock);
+ spin_lock(&inode_lru_lock);
if (inode != list_entry(inode_lru.next,
struct inode, i_lru))
continue; /* wrong inode or list_empty */
- spin_lock(&inode->i_lock);
+ /* avoid lock inversions with trylock */
+ if (!spin_trylock(&inode->i_lock))
+ continue;
if (!can_unuse(inode)) {
spin_unlock(&inode->i_lock);
continue;
@@ -699,6 +711,7 @@ static void prune_icache(int nr_to_scan)
__count_vm_events(KSWAPD_INODESTEAL, reap);
else
__count_vm_events(PGINODESTEAL, reap);
+ spin_unlock(&inode_lru_lock);
spin_unlock(&inode_lock);
dispose_list(&freeable);
--
1.7.1
--
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