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SubjectRe: [PATCH 3/4] fs: Lock the inode LRU list separately
  some typos

On the 27.10.2010 06:23, Dave Chinner wrote:
> From: Dave Chinner<dchinner@redhat.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@redhat.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
, then just move
or
, then move
> + * 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.
cannot
> */
> - 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);



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