[PATCH 0/3] fs: peel back the inode_lock some more

[PATCH 0/3] fs: peel back the inode_lock some more

[Dave Chinner]

Hi Al,

These as the first versions of the patches that remove the inode
lock from the writeback lists, superblock inode lists and the inode
hash table. I haven't polished them at all, but they appear to work
ok so I thought I'd send them out for comments before I went to bed...

With these patches the inode_lock pretty much disappears from my
lock_stat profiles, with the writeback list lock being the most
contended of the replacements on an 8-way machine.

Cheers,

Dave.

[PATCH 1/3] fs: move i_sb_list out from under inode_lock

[Dave Chinner]

From: Dave Chinner <dchinner@redhat.com>

Protect the per-sb inode list with a new global lock
inode_sb_list_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/drop_caches.c       |    9 +++++----
 fs/fs-writeback.c      |   21 +++++++++++----------
 fs/inode.c             |   43 +++++++++++++++++++++++--------------------
 fs/internal.h          |    2 ++
 fs/notify/inode_mark.c |   15 ++++++++-------
 fs/quota/dquot.c       |   28 ++++++++++++++++------------
 6 files changed, 65 insertions(+), 53 deletions(-)

diff --git a/fs/drop_caches.c b/fs/drop_caches.c
index 62dd8ee..86cd2f1 100644
--- a/fs/drop_caches.c
+++ b/fs/drop_caches.c
@@ -8,6 +8,7 @@
 #include <linux/writeback.h>
 #include <linux/sysctl.h>
 #include <linux/gfp.h>
+#include "internal.h"
 
 /* A global variable is a bit ugly, but it keeps the code simple */
 int sysctl_drop_caches;
@@ -16,7 +17,7 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 {
 	struct inode *inode, *toput_inode = NULL;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		spin_lock(&inode->i_lock);
 		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
@@ -26,13 +27,13 @@ static void drop_pagecache_sb(struct super_block *sb, void *unused)
 		}
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_sb_list_lock);
 		invalidate_mapping_pages(inode->i_mapping, 0, -1);
 		iput(toput_inode);
 		toput_inode = inode;
-		spin_lock(&inode_lock);
+		spin_lock(&inode_sb_list_lock);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 	iput(toput_inode);
 }
 
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 50de4f1..7707a62 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1053,7 +1053,7 @@ static void wait_sb_inodes(struct super_block *sb)
 	 */
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 
 	/*
 	 * Data integrity sync. Must wait for all pages under writeback,
@@ -1073,14 +1073,15 @@ static void wait_sb_inodes(struct super_block *sb)
 		}
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_sb_list_lock);
+
 		/*
-		 * We hold a reference to 'inode' so it couldn't have
-		 * been removed from s_inodes list while we dropped the
-		 * inode_lock.  We cannot iput the inode now as we can
-		 * be holding the last reference and we cannot iput it
-		 * under inode_lock. So we keep the reference and iput
-		 * it later.
+		 * We hold a reference to 'inode' so it couldn't have been
+		 * removed from s_inodes list while we dropped the
+		 * inode_sb_list_lock.  We cannot iput the inode now as we can
+		 * be holding the last reference and we cannot iput it under
+		 * inode_sb_list_lock. So we keep the reference and iput it
+		 * later.
 		 */
 		iput(old_inode);
 		old_inode = inode;
@@ -1089,9 +1090,9 @@ static void wait_sb_inodes(struct super_block *sb)
 
 		cond_resched();
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_sb_list_lock);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 	iput(old_inode);
 }
 
diff --git a/fs/inode.c b/fs/inode.c
index f64aeda..44f28dd 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -32,10 +32,15 @@
  *   inode->i_state, __iget()
  * inode_lru_lock protects:
  *   inode_lru, inode->i_lru
+ * inode_sb_list_lock protects:
+ *   sb->s_inodes, inode->i_sb_list
  *
  * Lock ordering:
  * inode_lock
  *   inode->i_lock
+ *
+ * inode_sb_list_lock
+ *   inode->i_lock
  *     inode_lru_lock
  */
 
@@ -97,6 +102,8 @@ static struct hlist_head *inode_hashtable __read_mostly;
  */
 DEFINE_SPINLOCK(inode_lock);
 
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_sb_list_lock);
+
 /*
  * iprune_sem provides exclusion between the kswapd or try_to_free_pages
  * icache shrinking path, and the umount path.  Without this exclusion,
@@ -365,26 +372,23 @@ static void inode_lru_list_del(struct inode *inode)
 	spin_unlock(&inode_lru_lock);
 }
 
-static inline void __inode_sb_list_add(struct inode *inode)
-{
-	list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
-}
-
 /**
  * inode_sb_list_add - add inode to the superblock list of inodes
  * @inode: inode to add
  */
 void inode_sb_list_add(struct inode *inode)
 {
-	spin_lock(&inode_lock);
-	__inode_sb_list_add(inode);
-	spin_unlock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
+	list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
+	spin_unlock(&inode_sb_list_lock);
 }
 EXPORT_SYMBOL_GPL(inode_sb_list_add);
 
-static inline void __inode_sb_list_del(struct inode *inode)
+static inline void inode_sb_list_del(struct inode *inode)
 {
+	spin_lock(&inode_sb_list_lock);
 	list_del_init(&inode->i_sb_list);
+	spin_unlock(&inode_sb_list_lock);
 }
 
 static unsigned long hash(struct super_block *sb, unsigned long hashval)
@@ -460,9 +464,10 @@ static void evict(struct inode *inode)
 
 	spin_lock(&inode_lock);
 	list_del_init(&inode->i_wb_list);
-	__inode_sb_list_del(inode);
 	spin_unlock(&inode_lock);
 
+	inode_sb_list_del(inode);
+
 	if (op->evict_inode) {
 		op->evict_inode(inode);
 	} else {
@@ -516,7 +521,7 @@ void evict_inodes(struct super_block *sb)
 
 	down_write(&iprune_sem);
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
 		if (atomic_read(&inode->i_count))
 			continue;
@@ -534,7 +539,7 @@ void evict_inodes(struct super_block *sb)
 
 		list_add(&inode->i_lru, &dispose);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 
 	dispose_list(&dispose);
 	up_write(&iprune_sem);
@@ -555,7 +560,7 @@ int invalidate_inodes(struct super_block *sb)
 
 	down_write(&iprune_sem);
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
 		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
@@ -574,7 +579,7 @@ int invalidate_inodes(struct super_block *sb)
 
 		list_add(&inode->i_lru, &dispose);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 
 	dispose_list(&dispose);
 	up_write(&iprune_sem);
@@ -839,16 +844,14 @@ struct inode *new_inode(struct super_block *sb)
 {
 	struct inode *inode;
 
-	spin_lock_prefetch(&inode_lock);
+	spin_lock_prefetch(&inode_sb_list_lock);
 
 	inode = alloc_inode(sb);
 	if (inode) {
-		spin_lock(&inode_lock);
 		spin_lock(&inode->i_lock);
 		inode->i_state = 0;
 		spin_unlock(&inode->i_lock);
-		__inode_sb_list_add(inode);
-		spin_unlock(&inode_lock);
+		inode_sb_list_add(inode);
 	}
 	return inode;
 }
@@ -918,7 +921,7 @@ static struct inode *get_new_inode(struct super_block *sb,
 			inode->i_state = I_NEW;
 			spin_unlock(&inode->i_lock);
 			hlist_add_head(&inode->i_hash, head);
-			__inode_sb_list_add(inode);
+			inode_sb_list_add(inode);
 			spin_unlock(&inode_lock);
 
 			/* Return the locked inode with I_NEW set, the
@@ -967,7 +970,7 @@ static struct inode *get_new_inode_fast(struct super_block *sb,
 			inode->i_state = I_NEW;
 			spin_unlock(&inode->i_lock);
 			hlist_add_head(&inode->i_hash, head);
-			__inode_sb_list_add(inode);
+			inode_sb_list_add(inode);
 			spin_unlock(&inode_lock);
 
 			/* Return the locked inode with I_NEW set, the
diff --git a/fs/internal.h b/fs/internal.h
index ebad3b9..493baa1 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -108,3 +108,5 @@ extern void release_open_intent(struct nameidata *);
 extern int get_nr_dirty_inodes(void);
 extern int evict_inodes(struct super_block *);
 extern int invalidate_inodes(struct super_block *);
+
+extern spinlock_t inode_sb_list_lock;
diff --git a/fs/notify/inode_mark.c b/fs/notify/inode_mark.c
index 9c0fb09..06c8216 100644
--- a/fs/notify/inode_mark.c
+++ b/fs/notify/inode_mark.c
@@ -29,6 +29,8 @@
 #include <linux/fsnotify_backend.h>
 #include "fsnotify.h"
 
+#include "../internal.h"
+
 /*
  * Recalculate the mask of events relevant to a given inode locked.
  */
@@ -232,15 +234,14 @@ out:
  * fsnotify_unmount_inodes - an sb is unmounting.  handle any watched inodes.
  * @list: list of inodes being unmounted (sb->s_inodes)
  *
- * Called with inode_lock held, protecting the unmounting super block's list
- * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay.
- * We temporarily drop inode_lock, however, and CAN block.
+ * Called during unmount with no locks held, so needs to be safe against
+ * concurrent modifiers. We temporarily drop inode_sb_list_lock and CAN block.
  */
 void fsnotify_unmount_inodes(struct list_head *list)
 {
 	struct inode *inode, *next_i, *need_iput = NULL;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry_safe(inode, next_i, list, i_sb_list) {
 		struct inode *need_iput_tmp;
 
@@ -293,7 +294,7 @@ void fsnotify_unmount_inodes(struct list_head *list)
 		 * will be added since the umount has begun.  Finally,
 		 * iprune_mutex keeps shrink_icache_memory() away.
 		 */
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_sb_list_lock);
 
 		if (need_iput_tmp)
 			iput(need_iput_tmp);
@@ -305,7 +306,7 @@ void fsnotify_unmount_inodes(struct list_head *list)
 
 		iput(inode);
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_sb_list_lock);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 }
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index a2d89f8..440f64c 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -76,7 +76,7 @@
 #include <linux/buffer_head.h>
 #include <linux/capability.h>
 #include <linux/quotaops.h>
-#include <linux/writeback.h> /* for inode_lock, oddly enough.. */
+#include "../internal.h" /* ugh */
 
 #include <asm/uaccess.h>
 
@@ -896,7 +896,7 @@ static void add_dquot_ref(struct super_block *sb, int type)
 	int reserved = 0;
 #endif
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		spin_lock(&inode->i_lock);
 		if ((inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) ||
@@ -911,19 +911,23 @@ static void add_dquot_ref(struct super_block *sb, int type)
 #endif
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_sb_list_lock);
 
 		iput(old_inode);
 		__dquot_initialize(inode, type);
-		/* We hold a reference to 'inode' so it couldn't have been
-		 * removed from s_inodes list while we dropped the inode_lock.
-		 * We cannot iput the inode now as we can be holding the last
-		 * reference and we cannot iput it under inode_lock. So we
-		 * keep the reference and iput it later. */
+
+		/*
+		 * We hold a reference to 'inode' so it couldn't have been
+		 * removed from s_inodes list while we dropped the
+		 * inode_sb_list_lock We cannot iput the inode now as we can be
+		 * holding the last reference and we cannot iput it under
+		 * inode_sb_list_lock. So we keep the reference and iput it
+		 * later.
+		 */
 		old_inode = inode;
-		spin_lock(&inode_lock);
+		spin_lock(&inode_sb_list_lock);
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 	iput(old_inode);
 
 #ifdef CONFIG_QUOTA_DEBUG
@@ -1004,7 +1008,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
 	struct inode *inode;
 	int reserved = 0;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_sb_list_lock);
 	list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
 		/*
 		 *  We have to scan also I_NEW inodes because they can already
@@ -1018,7 +1022,7 @@ static void remove_dquot_ref(struct super_block *sb, int type,
 			remove_inode_dquot_ref(inode, type, tofree_head);
 		}
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_sb_list_lock);
 #ifdef CONFIG_QUOTA_DEBUG
 	if (reserved) {
 		printk(KERN_WARNING "VFS (%s): Writes happened after quota"
-- 
1.7.1

[PATCH 2/3] fs: move i_wb_list out from under inode_lock

[Dave Chinner]

From: Dave Chinner <dchinner@redhat.com>

Protect the inode writeback list with a new global lock
inode_wb_list_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/block_dev.c            |    4 +-
 fs/fs-writeback.c         |  152 ++++++++++++++++++++++++---------------------
 fs/inode.c                |   12 +++-
 fs/internal.h             |    7 ++-
 include/linux/writeback.h |    1 +
 mm/backing-dev.c          |    8 +-
 6 files changed, 103 insertions(+), 81 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index dea3b62..a94cbf0 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -56,11 +56,11 @@ EXPORT_SYMBOL(I_BDEV);
 static void bdev_inode_switch_bdi(struct inode *inode,
 			struct backing_dev_info *dst)
 {
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	inode->i_data.backing_dev_info = dst;
 	if (inode->i_state & I_DIRTY)
 		list_move(&inode->i_wb_list, &dst->wb.b_dirty);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 }
 
 static sector_t max_block(struct block_device *bdev)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 7707a62..5b7cb95 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -162,6 +162,17 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
 }
 
 /*
+ * Remove the inode from the writeback list it is on.
+ */
+void inode_wb_list_del(struct inode *inode)
+{
+	spin_lock(&inode_wb_list_lock);
+	list_del_init(&inode->i_wb_list);
+	spin_unlock(&inode_wb_list_lock);
+}
+
+
+/*
  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
  * furthest end of its superblock's dirty-inode list.
  *
@@ -174,6 +185,7 @@ static void redirty_tail(struct inode *inode)
 {
 	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
 
+	assert_spin_locked(&inode_wb_list_lock);
 	if (!list_empty(&wb->b_dirty)) {
 		struct inode *tail;
 
@@ -191,14 +203,17 @@ static void requeue_io(struct inode *inode)
 {
 	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
 
+	assert_spin_locked(&inode_wb_list_lock);
 	list_move(&inode->i_wb_list, &wb->b_more_io);
 }
 
 static void inode_sync_complete(struct inode *inode)
 {
 	/*
-	 * Prevent speculative execution through spin_unlock(&inode_lock);
+	 * Prevent speculative execution through
+	 * spin_unlock(&inode_wb_list_lock);
 	 */
+
 	smp_mb();
 	wake_up_bit(&inode->i_state, __I_SYNC);
 }
@@ -272,6 +287,7 @@ static void move_expired_inodes(struct list_head *delaying_queue,
  */
 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
 {
+	assert_spin_locked(&inode_wb_list_lock);
 	list_splice_init(&wb->b_more_io, &wb->b_io);
 	move_expired_inodes(&wb->b_dirty, &wb->b_io, older_than_this);
 }
@@ -294,25 +310,23 @@ static void inode_wait_for_writeback(struct inode *inode)
 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 	 while (inode->i_state & I_SYNC) {
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_wb_list_lock);
 		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
-		spin_lock(&inode_lock);
+		spin_lock(&inode_wb_list_lock);
 		spin_lock(&inode->i_lock);
 	}
 }
 
 /*
- * Write out an inode's dirty pages.  Called under inode_lock.  Either the
- * caller has ref on the inode (either via __iget or via syscall against an fd)
- * or the inode has I_WILL_FREE set (via generic_forget_inode)
+ * Write out an inode's dirty pages.  Called under inode_wb_list_lock.  Either
+ * the caller has ref on the inode (either via __iget or via syscall against an
+ * fd) or the inode has I_WILL_FREE set.
  *
  * If `wait' is set, wait on the writeout.
  *
  * The whole writeout design is quite complex and fragile.  We want to avoid
  * starvation of particular inodes when others are being redirtied, prevent
  * livelocks, etc.
- *
- * Called under inode_lock.
  */
 static int
 writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
@@ -354,7 +368,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	inode->i_state |= I_SYNC;
 	inode->i_state &= ~I_DIRTY_PAGES;
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 
 	ret = do_writepages(mapping, wbc);
 
@@ -374,12 +388,10 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 	 * due to delalloc, clear dirty metadata flags right before
 	 * write_inode()
 	 */
-	spin_lock(&inode_lock);
 	spin_lock(&inode->i_lock);
 	dirty = inode->i_state & I_DIRTY;
 	inode->i_state &= ~(I_DIRTY_SYNC | I_DIRTY_DATASYNC);
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_lock);
 	/* Don't write the inode if only I_DIRTY_PAGES was set */
 	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
 		int err = write_inode(inode, wbc);
@@ -387,7 +399,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 			ret = err;
 	}
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	spin_lock(&inode->i_lock);
 	inode->i_state &= ~I_SYNC;
 	if (!(inode->i_state & I_FREEING)) {
@@ -529,10 +541,10 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
 			 */
 			redirty_tail(inode);
 		}
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_wb_list_lock);
 		iput(inode);
 		cond_resched();
-		spin_lock(&inode_lock);
+		spin_lock(&inode_wb_list_lock);
 		if (wbc->nr_to_write <= 0) {
 			wbc->more_io = 1;
 			return 1;
@@ -551,7 +563,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
 
 	if (!wbc->wb_start)
 		wbc->wb_start = jiffies; /* livelock avoidance */
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	if (!wbc->for_kupdate || list_empty(&wb->b_io))
 		queue_io(wb, wbc->older_than_this);
 
@@ -569,7 +581,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
 		if (ret)
 			break;
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 	/* Leave any unwritten inodes on b_io */
 }
 
@@ -578,11 +590,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
 {
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	if (!wbc->for_kupdate || list_empty(&wb->b_io))
 		queue_io(wb, wbc->older_than_this);
 	writeback_sb_inodes(sb, wb, wbc, true);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 }
 
 /*
@@ -692,7 +704,7 @@ static long wb_writeback(struct bdi_writeback *wb,
 		 * become available for writeback. Otherwise
 		 * we'll just busyloop.
 		 */
-		spin_lock(&inode_lock);
+		spin_lock(&inode_wb_list_lock);
 		if (!list_empty(&wb->b_more_io))  {
 			inode = wb_inode(wb->b_more_io.prev);
 			trace_wbc_writeback_wait(&wbc, wb->bdi);
@@ -700,7 +712,7 @@ static long wb_writeback(struct bdi_writeback *wb,
 			inode_wait_for_writeback(inode);
 			spin_unlock(&inode->i_lock);
 		}
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_wb_list_lock);
 	}
 
 	return wrote;
@@ -940,6 +952,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 	struct super_block *sb = inode->i_sb;
 	struct backing_dev_info *bdi = NULL;
 	bool wakeup_bdi = false;
+	int was_dirty;
 
 	/*
 	 * Don't do this for I_DIRTY_PAGES - that doesn't actually
@@ -963,63 +976,62 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 	if (unlikely(block_dump))
 		block_dump___mark_inode_dirty(inode);
 
-	spin_lock(&inode_lock);
 	spin_lock(&inode->i_lock);
-	if ((inode->i_state & flags) != flags) {
-		const int was_dirty = inode->i_state & I_DIRTY;
+	if ((inode->i_state & flags) == flags)
+		goto out_unlock_inode;
 
-		inode->i_state |= flags;
+	was_dirty = inode->i_state & I_DIRTY;
+	inode->i_state |= flags;
 
-		/*
-		 * If the inode is being synced, just update its dirty state.
-		 * The unlocker will place the inode on the appropriate
-		 * superblock list, based upon its state.
-		 */
-		if (inode->i_state & I_SYNC)
-			goto out_unlock_inode;
+	/*
+	 * If the inode is being synced, just update its dirty state.
+	 * The unlocker will place the inode on the appropriate
+	 * superblock list, based upon its state.
+	 */
+	if (inode->i_state & I_SYNC)
+		goto out_unlock_inode;
 
-		/*
-		 * Only add valid (hashed) inodes to the superblock's
-		 * dirty list.  Add blockdev inodes as well.
-		 */
-		if (!S_ISBLK(inode->i_mode)) {
-			if (inode_unhashed(inode))
-				goto out_unlock_inode;
-		}
-		if (inode->i_state & I_FREEING)
+	/*
+	 * Only add valid (hashed) inodes to the superblock's
+	 * dirty list.  Add blockdev inodes as well.
+	 */
+	if (!S_ISBLK(inode->i_mode)) {
+		if (inode_unhashed(inode))
 			goto out_unlock_inode;
+	}
+	if (inode->i_state & I_FREEING)
+		goto out_unlock_inode;
 
+	/*
+	 * If the inode was already on b_dirty/b_io/b_more_io, don't
+	 * reposition it (that would break b_dirty time-ordering).
+	 */
+	if (was_dirty) {
+out_unlock_inode:
 		spin_unlock(&inode->i_lock);
-		/*
-		 * If the inode was already on b_dirty/b_io/b_more_io, don't
-		 * reposition it (that would break b_dirty time-ordering).
-		 */
-		if (!was_dirty) {
-			bdi = inode_to_bdi(inode);
+		return;
+	}
 
-			if (bdi_cap_writeback_dirty(bdi)) {
-				WARN(!test_bit(BDI_registered, &bdi->state),
-				     "bdi-%s not registered\n", bdi->name);
+	spin_unlock(&inode->i_lock);
+	bdi = inode_to_bdi(inode);
 
-				/*
-				 * If this is the first dirty inode for this
-				 * bdi, we have to wake-up the corresponding
-				 * bdi thread to make sure background
-				 * write-back happens later.
-				 */
-				if (!wb_has_dirty_io(&bdi->wb))
-					wakeup_bdi = true;
-			}
+	if (bdi_cap_writeback_dirty(bdi)) {
+		WARN(!test_bit(BDI_registered, &bdi->state),
+		     "bdi-%s not registered\n", bdi->name);
 
-			inode->dirtied_when = jiffies;
-			list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
-		}
-		goto out;
+		/*
+		 * If this is the first dirty inode for this bdi, we have to
+		 * wake-up the corresponding bdi thread to make sure background
+		 * write-back happens later.
+		 */
+		if (!wb_has_dirty_io(&bdi->wb))
+			wakeup_bdi = true;
 	}
-out_unlock_inode:
-	spin_unlock(&inode->i_lock);
-out:
-	spin_unlock(&inode_lock);
+
+	spin_lock(&inode_wb_list_lock);
+	inode->dirtied_when = jiffies;
+	list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
+	spin_unlock(&inode_wb_list_lock);
 
 	if (wakeup_bdi)
 		bdi_wakeup_thread_delayed(bdi);
@@ -1195,9 +1207,9 @@ int write_inode_now(struct inode *inode, int sync)
 		wbc.nr_to_write = 0;
 
 	might_sleep();
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	ret = writeback_single_inode(inode, &wbc);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 	if (sync)
 		inode_sync_wait(inode);
 	return ret;
@@ -1219,9 +1231,9 @@ int sync_inode(struct inode *inode, struct writeback_control *wbc)
 {
 	int ret;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	ret = writeback_single_inode(inode, wbc);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 	return ret;
 }
 EXPORT_SYMBOL(sync_inode);
diff --git a/fs/inode.c b/fs/inode.c
index 44f28dd..130aa74 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -24,6 +24,7 @@
 #include <linux/mount.h>
 #include <linux/async.h>
 #include <linux/posix_acl.h>
+#include "internal.h"
 
 /*
  * inode locking rules.
@@ -34,6 +35,8 @@
  *   inode_lru, inode->i_lru
  * inode_sb_list_lock protects:
  *   sb->s_inodes, inode->i_sb_list
+ * inode_sb_list_lock protects:
+ *   bdi->wb.b_{dirty,io,more_io}, inode->i_wb_list
  *
  * Lock ordering:
  * inode_lock
@@ -42,6 +45,9 @@
  * inode_sb_list_lock
  *   inode->i_lock
  *     inode_lru_lock
+ *
+ * inode_wb_list_lock
+ *   inode->i_lock
  */
 
 /*
@@ -103,6 +109,7 @@ static struct hlist_head *inode_hashtable __read_mostly;
 DEFINE_SPINLOCK(inode_lock);
 
 __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_sb_list_lock);
+__cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_wb_list_lock);
 
 /*
  * iprune_sem provides exclusion between the kswapd or try_to_free_pages
@@ -462,10 +469,7 @@ static void evict(struct inode *inode)
 
 	BUG_ON(!(inode->i_state & I_FREEING));
 
-	spin_lock(&inode_lock);
-	list_del_init(&inode->i_wb_list);
-	spin_unlock(&inode_lock);
-
+	inode_wb_list_del(inode);
 	inode_sb_list_del(inode);
 
 	if (op->evict_inode) {
diff --git a/fs/internal.h b/fs/internal.h
index 493baa1..fd3f700 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -106,7 +106,12 @@ extern void release_open_intent(struct nameidata *);
  * inode.c
  */
 extern int get_nr_dirty_inodes(void);
-extern int evict_inodes(struct super_block *);
+extern void evict_inodes(struct super_block *);
 extern int invalidate_inodes(struct super_block *);
 
 extern spinlock_t inode_sb_list_lock;
+
+/*
+ * fs-writeback.c
+ */
+extern void inode_wb_list_del(struct inode *inode);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 242b6f8..e78a240 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -10,6 +10,7 @@
 struct backing_dev_info;
 
 extern spinlock_t inode_lock;
+extern spinlock_t inode_wb_list_lock;
 
 /*
  * fs/fs-writeback.c
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 15d5097..168ba5e 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -73,14 +73,14 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
 	struct inode *inode;
 
 	nr_wb = nr_dirty = nr_io = nr_more_io = 0;
-	spin_lock(&inode_lock);
+	spin_lock(&inode_wb_list_lock);
 	list_for_each_entry(inode, &wb->b_dirty, i_wb_list)
 		nr_dirty++;
 	list_for_each_entry(inode, &wb->b_io, i_wb_list)
 		nr_io++;
 	list_for_each_entry(inode, &wb->b_more_io, i_wb_list)
 		nr_more_io++;
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_wb_list_lock);
 
 	global_dirty_limits(&background_thresh, &dirty_thresh);
 	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
@@ -682,11 +682,11 @@ void bdi_destroy(struct backing_dev_info *bdi)
 	if (bdi_has_dirty_io(bdi)) {
 		struct bdi_writeback *dst = &default_backing_dev_info.wb;
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_wb_list_lock);
 		list_splice(&bdi->wb.b_dirty, &dst->b_dirty);
 		list_splice(&bdi->wb.b_io, &dst->b_io);
 		list_splice(&bdi->wb.b_more_io, &dst->b_more_io);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_wb_list_lock);
 	}
 
 	bdi_unregister(bdi);
-- 
1.7.1

[PATCH 3/3] fs: move i_hash out from under inode_lock

[Dave Chinner]

From: Dave Chinner <dchinner@redhat.com>

Protect the inode hash lists with a new global lock
inode_hash_lock and use it to protect the list manipulations and
traversals. This lock replaces the inode_lock as the inodes on the
list can be validity checked while holding the inode->i_lock and
hence the inode_lock is no longer needed to protect the lists.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 fs/inode.c |   69 ++++++++++++++++++++++++++++++++++-------------------------
 1 files changed, 40 insertions(+), 29 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 130aa74..738ba4e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -37,6 +37,8 @@
  *   sb->s_inodes, inode->i_sb_list
  * inode_sb_list_lock protects:
  *   bdi->wb.b_{dirty,io,more_io}, inode->i_wb_list
+ * inode_hash_lock protects:
+ *   inode_hashtable, inode->i_hash
  *
  * Lock ordering:
  * inode_lock
@@ -48,6 +50,12 @@
  *
  * inode_wb_list_lock
  *   inode->i_lock
+ *
+ * inode_hash_lock
+ *   inode->i_lock
+ *
+ * iunique_lock
+ *   inode_hash_lock
  */
 
 /*
@@ -83,6 +91,8 @@
 
 static unsigned int i_hash_mask __read_mostly;
 static unsigned int i_hash_shift __read_mostly;
+static struct hlist_head *inode_hashtable __read_mostly;
+static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);
 
 /*
  * Each inode can be on two separate lists. One is
@@ -98,7 +108,6 @@ 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;
 
 /*
  * A simple spinlock to protect the list manipulations.
@@ -420,9 +429,9 @@ void __insert_inode_hash(struct inode *inode, unsigned long hashval)
 {
 	struct hlist_head *b = inode_hashtable + hash(inode->i_sb, hashval);
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_hash_lock);
 	hlist_add_head(&inode->i_hash, b);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 }
 EXPORT_SYMBOL(__insert_inode_hash);
 
@@ -434,9 +443,9 @@ EXPORT_SYMBOL(__insert_inode_hash);
  */
 void remove_inode_hash(struct inode *inode)
 {
-	spin_lock(&inode_lock);
+	spin_lock(&inode_hash_lock);
 	hlist_del_init(&inode->i_hash);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 }
 EXPORT_SYMBOL(remove_inode_hash);
 
@@ -914,7 +923,7 @@ static struct inode *get_new_inode(struct super_block *sb,
 	if (inode) {
 		struct inode *old;
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_hash_lock);
 		/* We released the lock, so.. */
 		old = find_inode(sb, head, test, data);
 		if (!old) {
@@ -925,8 +934,8 @@ static struct inode *get_new_inode(struct super_block *sb,
 			inode->i_state = I_NEW;
 			spin_unlock(&inode->i_lock);
 			hlist_add_head(&inode->i_hash, head);
+			spin_unlock(&inode_hash_lock);
 			inode_sb_list_add(inode);
-			spin_unlock(&inode_lock);
 
 			/* Return the locked inode with I_NEW set, the
 			 * caller is responsible for filling in the contents
@@ -939,7 +948,7 @@ static struct inode *get_new_inode(struct super_block *sb,
 		 * us. Use the old inode instead of the one we just
 		 * allocated.
 		 */
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		destroy_inode(inode);
 		inode = old;
 		wait_on_inode(inode);
@@ -947,7 +956,7 @@ static struct inode *get_new_inode(struct super_block *sb,
 	return inode;
 
 set_failed:
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 	destroy_inode(inode);
 	return NULL;
 }
@@ -965,7 +974,7 @@ static struct inode *get_new_inode_fast(struct super_block *sb,
 	if (inode) {
 		struct inode *old;
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_hash_lock);
 		/* We released the lock, so.. */
 		old = find_inode_fast(sb, head, ino);
 		if (!old) {
@@ -974,8 +983,8 @@ static struct inode *get_new_inode_fast(struct super_block *sb,
 			inode->i_state = I_NEW;
 			spin_unlock(&inode->i_lock);
 			hlist_add_head(&inode->i_hash, head);
+			spin_unlock(&inode_hash_lock);
 			inode_sb_list_add(inode);
-			spin_unlock(&inode_lock);
 
 			/* Return the locked inode with I_NEW set, the
 			 * caller is responsible for filling in the contents
@@ -988,7 +997,7 @@ static struct inode *get_new_inode_fast(struct super_block *sb,
 		 * us. Use the old inode instead of the one we just
 		 * allocated.
 		 */
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		destroy_inode(inode);
 		inode = old;
 		wait_on_inode(inode);
@@ -1009,10 +1018,14 @@ static int test_inode_iunique(struct super_block *sb, unsigned long ino)
 	struct hlist_node *node;
 	struct inode *inode;
 
+	spin_lock(&inode_hash_lock);
 	hlist_for_each_entry(inode, node, b, i_hash) {
-		if (inode->i_ino == ino && inode->i_sb == sb)
+		if (inode->i_ino == ino && inode->i_sb == sb) {
+			spin_unlock(&inode_hash_lock);
 			return 0;
+		}
 	}
+	spin_unlock(&inode_hash_lock);
 
 	return 1;
 }
@@ -1042,7 +1055,6 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
 	static unsigned int counter;
 	ino_t res;
 
-	spin_lock(&inode_lock);
 	spin_lock(&iunique_lock);
 	do {
 		if (counter <= max_reserved)
@@ -1050,7 +1062,6 @@ ino_t iunique(struct super_block *sb, ino_t max_reserved)
 		res = counter++;
 	} while (!test_inode_iunique(sb, res));
 	spin_unlock(&iunique_lock);
-	spin_unlock(&inode_lock);
 
 	return res;
 }
@@ -1102,15 +1113,15 @@ static struct inode *ifind(struct super_block *sb,
 {
 	struct inode *inode;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_hash_lock);
 	inode = find_inode(sb, head, test, data);
 	if (inode) {
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		if (likely(wait))
 			wait_on_inode(inode);
 		return inode;
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 	return NULL;
 }
 
@@ -1134,14 +1145,14 @@ static struct inode *ifind_fast(struct super_block *sb,
 {
 	struct inode *inode;
 
-	spin_lock(&inode_lock);
+	spin_lock(&inode_hash_lock);
 	inode = find_inode_fast(sb, head, ino);
 	if (inode) {
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		wait_on_inode(inode);
 		return inode;
 	}
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 	return NULL;
 }
 
@@ -1306,7 +1317,7 @@ int insert_inode_locked(struct inode *inode)
 	while (1) {
 		struct hlist_node *node;
 		struct inode *old = NULL;
-		spin_lock(&inode_lock);
+		spin_lock(&inode_hash_lock);
 		hlist_for_each_entry(old, node, head, i_hash) {
 			if (old->i_ino != ino)
 				continue;
@@ -1321,12 +1332,12 @@ int insert_inode_locked(struct inode *inode)
 		}
 		if (likely(!node)) {
 			hlist_add_head(&inode->i_hash, head);
-			spin_unlock(&inode_lock);
+			spin_unlock(&inode_hash_lock);
 			return 0;
 		}
 		__iget(old);
 		spin_unlock(&old->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		wait_on_inode(old);
 		if (unlikely(!inode_unhashed(old))) {
 			iput(old);
@@ -1351,7 +1362,7 @@ int insert_inode_locked4(struct inode *inode, unsigned long hashval,
 		struct hlist_node *node;
 		struct inode *old = NULL;
 
-		spin_lock(&inode_lock);
+		spin_lock(&inode_hash_lock);
 		hlist_for_each_entry(old, node, head, i_hash) {
 			if (old->i_sb != sb)
 				continue;
@@ -1366,12 +1377,12 @@ int insert_inode_locked4(struct inode *inode, unsigned long hashval,
 		}
 		if (likely(!node)) {
 			hlist_add_head(&inode->i_hash, head);
-			spin_unlock(&inode_lock);
+			spin_unlock(&inode_hash_lock);
 			return 0;
 		}
 		__iget(old);
 		spin_unlock(&old->i_lock);
-		spin_unlock(&inode_lock);
+		spin_unlock(&inode_hash_lock);
 		wait_on_inode(old);
 		if (unlikely(!inode_unhashed(old))) {
 			iput(old);
@@ -1651,10 +1662,10 @@ static void __wait_on_freeing_inode(struct inode *inode)
 	wq = bit_waitqueue(&inode->i_state, __I_NEW);
 	prepare_to_wait(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_lock);
+	spin_unlock(&inode_hash_lock);
 	schedule();
 	finish_wait(wq, &wait.wait);
-	spin_lock(&inode_lock);
+	spin_lock(&inode_hash_lock);
 }
 
 static __initdata unsigned long ihash_entries;
-- 
1.7.1

Re: [PATCH 0/3] fs: peel back the inode_lock some more

[Christoph Hellwig]

Shouldn't inode_lock be completely gone after these?

also I hope moving to global locks really is just a step inbetween.
Especially for writeback I doubt moving from inode_lock to another
global lock makes a whole lot of difference - nevermind that it's
not too smart to lock per-object lists with a global lock.

Re: [PATCH 1/3] fs: move i_sb_list out from under inode_lock

[Christoph Hellwig]

Re: [PATCH 2/3] fs: move i_wb_list out from under inode_lock

[Christoph Hellwig]

> + * Write out an inode's dirty pages.  Called under inode_wb_list_lock.  Either
> + * the caller has ref on the inode (either via __iget or via syscall against an
> + * fd) or the inode has I_WILL_FREE set.

Just drop mentioning of how we got the reference ,it's rather pointless.

>  writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
> @@ -354,7 +368,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
>  	inode->i_state |= I_SYNC;
>  	inode->i_state &= ~I_DIRTY_PAGES;
>  	spin_unlock(&inode->i_lock);
> -	spin_unlock(&inode_lock);
> +	spin_unlock(&inode_wb_list_lock);

We don't actually need inode_wb_list_lock here.  But I guess we can
fix this later and be conservative for now.

> @@ -963,63 +976,62 @@ void __mark_inode_dirty(struct inode *inode, int flags)

I think the __mark_inode_dirty cleanup should be a separate patch,
it's rather confusing in the current form.

> +	if (was_dirty) {
> +out_unlock_inode:
>  		spin_unlock(&inode->i_lock);
> +		return;
> +	}

Please just move the label to the end of the function and add another
goto here.

Re: [PATCH 3/3] fs: move i_hash out from under inode_lock

[Christoph Hellwig]

> @@ -925,8 +934,8 @@ static struct inode *get_new_inode(struct super_block *sb,
>  			inode->i_state = I_NEW;
>  			spin_unlock(&inode->i_lock);
>  			hlist_add_head(&inode->i_hash, head);
> +			spin_unlock(&inode_hash_lock);
>  			inode_sb_list_add(inode);
> -			spin_unlock(&inode_lock);

Al said he wanted to have the sb lock nest inside the hash lock for now
I think.  Doubt it matters much, but it keeps the behaviour that we
can't look up an inode which is not added to the per-sb list yet.

After that a better patch description might be:

	"rename inode_lock to inode_hash_lock"

as the inode_lock coverage after the previous patches should be 100%
identical to the new hash lock.

Re: [PATCH 2/3] fs: move i_wb_list out from under inode_lock

[Dave Chinner]

On Thu, Oct 28, 2010 at 10:19:49AM -0400, Christoph Hellwig wrote:
> > + * Write out an inode's dirty pages.  Called under inode_wb_list_lock.  Either
> > + * the caller has ref on the inode (either via __iget or via syscall against an
> > + * fd) or the inode has I_WILL_FREE set.
> 
> Just drop mentioning of how we got the reference ,it's rather pointless.

OK.

> >  writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
> > @@ -354,7 +368,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
> >  	inode->i_state |= I_SYNC;
> >  	inode->i_state &= ~I_DIRTY_PAGES;
> >  	spin_unlock(&inode->i_lock);
> > -	spin_unlock(&inode_lock);
> > +	spin_unlock(&inode_wb_list_lock);
> 
> We don't actually need inode_wb_list_lock here.  But I guess we can
> fix this later and be conservative for now.

Hmmm - I think you are right. However, there are lots of
opportunities for cleaning up the locking in this areaş so leaving
it for later is probably best.

> > @@ -963,63 +976,62 @@ void __mark_inode_dirty(struct inode *inode, int flags)
> 
> I think the __mark_inode_dirty cleanup should be a separate patch,
> it's rather confusing in the current form.

Ok. I'll leave it out for now - there's various other cleanups
needed here now as well (e.g. the unlocked flags check is not needed
to avoid a global lock anymore) so I'll leave that for later, too.

> > +	if (was_dirty) {
> > +out_unlock_inode:
> >  		spin_unlock(&inode->i_lock);
> > +		return;
> > +	}
> 
> Please just move the label to the end of the function and add another
> goto here.

Will do.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com