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fs: Lock the inode LRU list separately

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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@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Dave Chinner 2011-03-22 22:23:38 +11:00 committed by Al Viro
parent b2b2af8e61
commit 02afc410f3
1 changed files with 30 additions and 9 deletions
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39
fs/inode.c
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@ -32,10 +32,13 @@
*
* inode->i_lock protects:
* inode->i_state, inode->i_hash, __iget()
* inode_lru_lock protects:
* inode_lru, inode->i_lru
*
* Lock ordering:
* inode_lock
* inode->i_lock
* inode_lru_lock
*/
/*
@ -85,6 +88,7 @@ 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;
/*
@ -356,18 +360,22 @@ EXPORT_SYMBOL(ihold);
static void inode_lru_list_add(struct inode *inode)
{
spin_lock(&inode_lru_lock);
if (list_empty(&inode->i_lru)) {
list_add(&inode->i_lru, &inode_lru);
inodes_stat.nr_unused++;
}
spin_unlock(&inode_lru_lock);
}
static void inode_lru_list_del(struct inode *inode)
{
spin_lock(&inode_lru_lock);
if (!list_empty(&inode->i_lru)) {
list_del_init(&inode->i_lru);
inodes_stat.nr_unused--;
}
spin_unlock(&inode_lru_lock);
}
static inline void __inode_sb_list_add(struct inode *inode)
@ -543,10 +551,9 @@ void evict_inodes(struct super_block *sb)
}
inode->i_state |= I_FREEING;
if (!(inode->i_state & (I_DIRTY | I_SYNC)))
inodes_stat.nr_unused--;
inode_lru_list_del(inode);
spin_unlock(&inode->i_lock);
list_move(&inode->i_lru, &dispose);
list_add(&inode->i_lru, &dispose);
}
spin_unlock(&inode_lock);
@ -596,10 +603,9 @@ int invalidate_inodes(struct super_block *sb, bool kill_dirty)
}
inode->i_state |= I_FREEING;
if (!(inode->i_state & (I_DIRTY | I_SYNC)))
inodes_stat.nr_unused--;
inode_lru_list_del(inode);
spin_unlock(&inode->i_lock);
list_move(&inode->i_lru, &dispose);
list_add(&inode->i_lru, &dispose);
}
spin_unlock(&inode_lock);
@ -623,7 +629,7 @@ static int can_unuse(struct inode *inode)
/*
* Scan `goal' inodes on the unused list for freeable ones. They are moved to a
* temporary list and then are freed outside inode_lock by dispose_list().
* temporary list and then are freed outside inode_lru_lock by dispose_list().
*
* Any inodes which are pinned purely because of attached pagecache have their
* pagecache removed. If the inode has metadata buffers attached to
@ -645,6 +651,7 @@ 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;
@ -653,11 +660,20 @@ 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);
@ -676,17 +692,21 @@ 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;
@ -703,6 +723,7 @@ 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);