Message-ID: <20110421071757.GA30781@infradead.org>
Date:	Thu, 21 Apr 2011 03:17:57 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>, Mel Gorman <mel@...ux.vnet.ibm.com>,
	Dave Chinner <david@...morbit.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Itaru Kitayama <kitayama@...bb4u.ne.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 0/6] writeback: moving expire targets for
 background/kupdate works

Here's the inode_wb_list_lock splitup against current mainline:

---
From: Christoph Hellwig <hch@....de>
Subject: [PATCH] writeback: split inode_wb_list_lock

Split the global inode_wb_list_lock into a per-bdi_writeback list_lock,
as it's currently the most contended lock in the system for metadata
heavy workloads.  I won't help for single-filesystem workloads for
which we'll need the I/O-less balance_dirty_pages, but at least we
can dedicate a cpu to spinning on each bdi now for larger systems.

Based on earlier patches from Nick Piggin and Dave Chinner.

Signed-off-by: Christoph Hellwig <hch@....de>

Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c	2011-04-21 08:31:44.512334499 +0200
+++ linux-2.6/fs/fs-writeback.c	2011-04-21 09:07:05.327511722 +0200
@@ -180,12 +180,13 @@ void bdi_start_background_writeback(stru
  */
 void inode_wb_list_del(struct inode *inode)
 {
-	spin_lock(&inode_wb_list_lock);
+	struct backing_dev_info *bdi = inode_to_bdi(inode);
+
+	spin_lock(&bdi->wb.list_lock);
 	list_del_init(&inode->i_wb_list);
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&bdi->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.
@@ -195,11 +196,9 @@ void inode_wb_list_del(struct inode *ino
  * the case then the inode must have been redirtied while it was being written
  * out and we don't reset its dirtied_when.
  */
-static void redirty_tail(struct inode *inode)
+static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
 {
-	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
-
-	assert_spin_locked(&inode_wb_list_lock);
+	assert_spin_locked(&wb->list_lock);
 	if (!list_empty(&wb->b_dirty)) {
 		struct inode *tail;
 
@@ -213,11 +212,9 @@ static void redirty_tail(struct inode *i
 /*
  * requeue inode for re-scanning after bdi->b_io list is exhausted.
  */
-static void requeue_io(struct inode *inode)
+static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
 {
-	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
-
-	assert_spin_locked(&inode_wb_list_lock);
+	assert_spin_locked(&wb->list_lock);
 	list_move(&inode->i_wb_list, &wb->b_more_io);
 }
 
@@ -225,7 +222,7 @@ static void inode_sync_complete(struct i
 {
 	/*
 	 * Prevent speculative execution through
-	 * spin_unlock(&inode_wb_list_lock);
+	 * spin_unlock(&wb->list_lock);
 	 */
 
 	smp_mb();
@@ -301,7 +298,7 @@ static void move_expired_inodes(struct l
  */
 static void queue_io(struct bdi_writeback *wb, unsigned long *older_than_this)
 {
-	assert_spin_locked(&inode_wb_list_lock);
+	assert_spin_locked(&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);
 }
@@ -316,7 +313,8 @@ static int write_inode(struct inode *ino
 /*
  * Wait for writeback on an inode to complete.
  */
-static void inode_wait_for_writeback(struct inode *inode)
+static void inode_wait_for_writeback(struct inode *inode,
+		struct bdi_writeback *wb)
 {
 	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
 	wait_queue_head_t *wqh;
@@ -324,15 +322,15 @@ static void inode_wait_for_writeback(str
 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
 	while (inode->i_state & I_SYNC) {
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_wb_list_lock);
+		spin_unlock(&wb->list_lock);
 		__wait_on_bit(wqh, &wq, inode_wait, TASK_UNINTERRUPTIBLE);
-		spin_lock(&inode_wb_list_lock);
+		spin_lock(&wb->list_lock);
 		spin_lock(&inode->i_lock);
 	}
 }
 
 /*
- * Write out an inode's dirty pages.  Called under inode_wb_list_lock and
+ * Write out an inode's dirty pages.  Called under wb->list_lock and
  * inode->i_lock.  Either the caller has an active reference on the inode or
  * the inode has I_WILL_FREE set.
  *
@@ -343,13 +341,14 @@ static void inode_wait_for_writeback(str
  * livelocks, etc.
  */
 static int
-writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
+writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
+		struct writeback_control *wbc)
 {
 	struct address_space *mapping = inode->i_mapping;
 	unsigned dirty;
 	int ret;
 
-	assert_spin_locked(&inode_wb_list_lock);
+	assert_spin_locked(&wb->list_lock);
 	assert_spin_locked(&inode->i_lock);
 
 	if (!atomic_read(&inode->i_count))
@@ -367,14 +366,14 @@ writeback_single_inode(struct inode *ino
 		 * completed a full scan of b_io.
 		 */
 		if (wbc->sync_mode != WB_SYNC_ALL) {
-			requeue_io(inode);
+			requeue_io(inode, wb);
 			return 0;
 		}
 
 		/*
 		 * It's a data-integrity sync.  We must wait.
 		 */
-		inode_wait_for_writeback(inode);
+		inode_wait_for_writeback(inode, wb);
 	}
 
 	BUG_ON(inode->i_state & I_SYNC);
@@ -383,7 +382,7 @@ writeback_single_inode(struct inode *ino
 	inode->i_state |= I_SYNC;
 	inode->i_state &= ~I_DIRTY_PAGES;
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 
 	ret = do_writepages(mapping, wbc);
 
@@ -414,7 +413,7 @@ writeback_single_inode(struct inode *ino
 			ret = err;
 	}
 
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&wb->list_lock);
 	spin_lock(&inode->i_lock);
 	inode->i_state &= ~I_SYNC;
 	if (!(inode->i_state & I_FREEING)) {
@@ -428,7 +427,7 @@ writeback_single_inode(struct inode *ino
 				/*
 				 * slice used up: queue for next turn
 				 */
-				requeue_io(inode);
+				requeue_io(inode, wb);
 			} else {
 				/*
 				 * Writeback blocked by something other than
@@ -437,7 +436,7 @@ writeback_single_inode(struct inode *ino
 				 * retrying writeback of the dirty page/inode
 				 * that cannot be performed immediately.
 				 */
-				redirty_tail(inode);
+				redirty_tail(inode, wb);
 			}
 		} else if (inode->i_state & I_DIRTY) {
 			/*
@@ -446,7 +445,7 @@ writeback_single_inode(struct inode *ino
 			 * submission or metadata updates after data IO
 			 * completion.
 			 */
-			redirty_tail(inode);
+			redirty_tail(inode, wb);
 		} else {
 			/*
 			 * The inode is clean.  At this point we either have
@@ -510,7 +509,7 @@ static int writeback_sb_inodes(struct su
 				 * superblock, move all inodes not belonging
 				 * to it back onto the dirty list.
 				 */
-				redirty_tail(inode);
+				redirty_tail(inode, wb);
 				continue;
 			}
 
@@ -530,7 +529,7 @@ static int writeback_sb_inodes(struct su
 		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 			spin_unlock(&inode->i_lock);
-			requeue_io(inode);
+			requeue_io(inode, wb);
 			continue;
 		}
 
@@ -546,19 +545,19 @@ static int writeback_sb_inodes(struct su
 		__iget(inode);
 
 		pages_skipped = wbc->pages_skipped;
-		writeback_single_inode(inode, wbc);
+		writeback_single_inode(inode, wb, wbc);
 		if (wbc->pages_skipped != pages_skipped) {
 			/*
 			 * writeback is not making progress due to locked
 			 * buffers.  Skip this inode for now.
 			 */
-			redirty_tail(inode);
+			redirty_tail(inode, wb);
 		}
 		spin_unlock(&inode->i_lock);
-		spin_unlock(&inode_wb_list_lock);
+		spin_unlock(&wb->list_lock);
 		iput(inode);
 		cond_resched();
-		spin_lock(&inode_wb_list_lock);
+		spin_lock(&wb->list_lock);
 		if (wbc->nr_to_write <= 0) {
 			wbc->more_io = 1;
 			return 1;
@@ -577,7 +576,7 @@ void writeback_inodes_wb(struct bdi_writ
 
 	if (!wbc->wb_start)
 		wbc->wb_start = jiffies; /* livelock avoidance */
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&wb->list_lock);
 	if (!wbc->for_kupdate || list_empty(&wb->b_io))
 		queue_io(wb, wbc->older_than_this);
 
@@ -586,7 +585,7 @@ void writeback_inodes_wb(struct bdi_writ
 		struct super_block *sb = inode->i_sb;
 
 		if (!pin_sb_for_writeback(sb)) {
-			requeue_io(inode);
+			requeue_io(inode, wb);
 			continue;
 		}
 		ret = writeback_sb_inodes(sb, wb, wbc, false);
@@ -595,7 +594,7 @@ void writeback_inodes_wb(struct bdi_writ
 		if (ret)
 			break;
 	}
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 	/* Leave any unwritten inodes on b_io */
 }
 
@@ -604,11 +603,11 @@ static void __writeback_inodes_sb(struct
 {
 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&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_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 }
 
 /*
@@ -747,15 +746,15 @@ static long wb_writeback(struct bdi_writ
 		 * become available for writeback. Otherwise
 		 * we'll just busyloop.
 		 */
-		spin_lock(&inode_wb_list_lock);
+		spin_lock(&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);
 			spin_lock(&inode->i_lock);
-			inode_wait_for_writeback(inode);
+			inode_wait_for_writeback(inode, wb);
 			spin_unlock(&inode->i_lock);
 		}
-		spin_unlock(&inode_wb_list_lock);
+		spin_unlock(&wb->list_lock);
 	}
 
 	return wrote;
@@ -1092,10 +1091,10 @@ void __mark_inode_dirty(struct inode *in
 			}
 
 			spin_unlock(&inode->i_lock);
-			spin_lock(&inode_wb_list_lock);
+			spin_lock(&bdi->wb.list_lock);
 			inode->dirtied_when = jiffies;
 			list_move(&inode->i_wb_list, &bdi->wb.b_dirty);
-			spin_unlock(&inode_wb_list_lock);
+			spin_unlock(&bdi->wb.list_lock);
 
 			if (wakeup_bdi)
 				bdi_wakeup_thread_delayed(bdi);
@@ -1296,6 +1295,7 @@ EXPORT_SYMBOL(sync_inodes_sb);
  */
 int write_inode_now(struct inode *inode, int sync)
 {
+	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
 	int ret;
 	struct writeback_control wbc = {
 		.nr_to_write = LONG_MAX,
@@ -1308,11 +1308,11 @@ int write_inode_now(struct inode *inode,
 		wbc.nr_to_write = 0;
 
 	might_sleep();
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&wb->list_lock);
 	spin_lock(&inode->i_lock);
-	ret = writeback_single_inode(inode, &wbc);
+	ret = writeback_single_inode(inode, wb, &wbc);
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 	if (sync)
 		inode_sync_wait(inode);
 	return ret;
@@ -1332,13 +1332,14 @@ EXPORT_SYMBOL(write_inode_now);
  */
 int sync_inode(struct inode *inode, struct writeback_control *wbc)
 {
+	struct bdi_writeback *wb = &inode_to_bdi(inode)->wb;
 	int ret;
 
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&wb->list_lock);
 	spin_lock(&inode->i_lock);
-	ret = writeback_single_inode(inode, wbc);
+	ret = writeback_single_inode(inode, wb, wbc);
 	spin_unlock(&inode->i_lock);
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 	return ret;
 }
 EXPORT_SYMBOL(sync_inode);
Index: linux-2.6/fs/inode.c
===================================================================
--- linux-2.6.orig/fs/inode.c	2011-04-21 08:31:40.172358011 +0200
+++ linux-2.6/fs/inode.c	2011-04-21 09:07:05.327511722 +0200
@@ -37,7 +37,7 @@
  *   inode_lru, inode->i_lru
  * inode_sb_list_lock protects:
  *   sb->s_inodes, inode->i_sb_list
- * inode_wb_list_lock protects:
+ * bdi->wb.list_lock protects:
  *   bdi->wb.b_{dirty,io,more_io}, inode->i_wb_list
  * inode_hash_lock protects:
  *   inode_hashtable, inode->i_hash
@@ -48,7 +48,7 @@
  *   inode->i_lock
  *     inode_lru_lock
  *
- * inode_wb_list_lock
+ * bdi->wb.list_lock
  *   inode->i_lock
  *
  * inode_hash_lock
@@ -111,7 +111,6 @@ static LIST_HEAD(inode_lru);
 static DEFINE_SPINLOCK(inode_lru_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 icache shrinking and the
Index: linux-2.6/include/linux/writeback.h
===================================================================
--- linux-2.6.orig/include/linux/writeback.h	2011-04-21 08:31:42.185680435 +0200
+++ linux-2.6/include/linux/writeback.h	2011-04-21 09:07:05.327511722 +0200
@@ -9,8 +9,6 @@
 
 struct backing_dev_info;
 
-extern spinlock_t inode_wb_list_lock;
-
 /*
  * fs/fs-writeback.c
  */
Index: linux-2.6/mm/backing-dev.c
===================================================================
--- linux-2.6.orig/mm/backing-dev.c	2011-04-21 08:31:44.532334389 +0200
+++ linux-2.6/mm/backing-dev.c	2011-04-21 09:07:05.327511722 +0200
@@ -45,6 +45,17 @@ static struct timer_list sync_supers_tim
 static int bdi_sync_supers(void *);
 static void sync_supers_timer_fn(unsigned long);
 
+void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2)
+{
+	if (wb1 < wb2) {
+		spin_lock(&wb1->list_lock);
+		spin_lock_nested(&wb2->list_lock, 1);
+	} else {
+		spin_lock(&wb2->list_lock);
+		spin_lock_nested(&wb1->list_lock, 1);
+	}
+}
+
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
@@ -67,14 +78,14 @@ static int bdi_debug_stats_show(struct s
 	struct inode *inode;
 
 	nr_wb = nr_dirty = nr_io = nr_more_io = 0;
-	spin_lock(&inode_wb_list_lock);
+	spin_lock(&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_wb_list_lock);
+	spin_unlock(&wb->list_lock);
 
 	global_dirty_limits(&background_thresh, &dirty_thresh);
 	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
@@ -628,6 +639,7 @@ static void bdi_wb_init(struct bdi_write
 	INIT_LIST_HEAD(&wb->b_dirty);
 	INIT_LIST_HEAD(&wb->b_io);
 	INIT_LIST_HEAD(&wb->b_more_io);
+	spin_lock_init(&wb->list_lock);
 	setup_timer(&wb->wakeup_timer, wakeup_timer_fn, (unsigned long)bdi);
 }
 
@@ -676,11 +688,12 @@ void bdi_destroy(struct backing_dev_info
 	if (bdi_has_dirty_io(bdi)) {
 		struct bdi_writeback *dst = &default_backing_dev_info.wb;
 
-		spin_lock(&inode_wb_list_lock);
+		bdi_lock_two(&bdi->wb, dst);
 		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_wb_list_lock);
+		spin_unlock(&bdi->wb.list_lock);
+		spin_unlock(&dst->list_lock);
 	}
 
 	bdi_unregister(bdi);
Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c	2011-04-21 08:31:42.159013915 +0200
+++ linux-2.6/mm/filemap.c	2011-04-21 09:07:05.330845037 +0200
@@ -80,7 +80,7 @@
  *  ->i_mutex
  *    ->i_alloc_sem             (various)
  *
- *  inode_wb_list_lock
+ *  bdi->wb.list_lock
  *    sb_lock			(fs/fs-writeback.c)
  *    ->mapping->tree_lock	(__sync_single_inode)
  *
@@ -98,9 +98,9 @@
  *    ->zone.lru_lock		(check_pte_range->isolate_lru_page)
  *    ->private_lock		(page_remove_rmap->set_page_dirty)
  *    ->tree_lock		(page_remove_rmap->set_page_dirty)
- *    inode_wb_list_lock	(page_remove_rmap->set_page_dirty)
+ *    bdi.wb->list_lock		(page_remove_rmap->set_page_dirty)
  *    ->inode->i_lock		(page_remove_rmap->set_page_dirty)
- *    inode_wb_list_lock	(zap_pte_range->set_page_dirty)
+ *    bdi.wb->list_lock	(zap_pte_range->set_page_dirty)
  *    ->inode->i_lock		(zap_pte_range->set_page_dirty)
  *    ->private_lock		(zap_pte_range->__set_page_dirty_buffers)
  *
Index: linux-2.6/mm/rmap.c
===================================================================
--- linux-2.6.orig/mm/rmap.c	2011-04-21 08:31:41.519017382 +0200
+++ linux-2.6/mm/rmap.c	2011-04-21 09:07:05.330845037 +0200
@@ -32,11 +32,11 @@
  *               mmlist_lock (in mmput, drain_mmlist and others)
  *               mapping->private_lock (in __set_page_dirty_buffers)
  *               inode->i_lock (in set_page_dirty's __mark_inode_dirty)
- *               inode_wb_list_lock (in set_page_dirty's __mark_inode_dirty)
+ *               bdi.wb->list_lock (in set_page_dirty's __mark_inode_dirty)
  *                 sb_lock (within inode_lock in fs/fs-writeback.c)
  *                 mapping->tree_lock (widely used, in set_page_dirty,
  *                           in arch-dependent flush_dcache_mmap_lock,
- *                           within inode_wb_list_lock in __sync_single_inode)
+ *                           within bdi.wb->list_lock in __sync_single_inode)
  *
  * (code doesn't rely on that order so it could be switched around)
  * ->tasklist_lock
Index: linux-2.6/fs/block_dev.c
===================================================================
--- linux-2.6.orig/fs/block_dev.c	2011-04-21 08:31:44.522334444 +0200
+++ linux-2.6/fs/block_dev.c	2011-04-21 09:07:05.330845037 +0200
@@ -55,13 +55,16 @@ EXPORT_SYMBOL(I_BDEV);
 static void bdev_inode_switch_bdi(struct inode *inode,
 			struct backing_dev_info *dst)
 {
-	spin_lock(&inode_wb_list_lock);
+	struct backing_dev_info *old = inode->i_data.backing_dev_info;
+
+	bdi_lock_two(&old->wb, &dst->wb);
 	spin_lock(&inode->i_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->i_lock);
-	spin_unlock(&inode_wb_list_lock);
+	spin_unlock(&old->wb.list_lock);
+	spin_unlock(&dst->wb.list_lock);
 }
 
 static sector_t max_block(struct block_device *bdev)
Index: linux-2.6/include/linux/backing-dev.h
===================================================================
--- linux-2.6.orig/include/linux/backing-dev.h	2011-04-21 08:31:42.202347013 +0200
+++ linux-2.6/include/linux/backing-dev.h	2011-04-21 09:07:05.330845037 +0200
@@ -57,6 +57,7 @@ struct bdi_writeback {
 	struct list_head b_dirty;	/* dirty inodes */
 	struct list_head b_io;		/* parked for writeback */
 	struct list_head b_more_io;	/* parked for more writeback */
+	spinlock_t list_lock;		/* protects the b_* lists. */
 };
 
 struct backing_dev_info {
@@ -106,6 +107,7 @@ int bdi_writeback_thread(void *data);
 int bdi_has_dirty_io(struct backing_dev_info *bdi);
 void bdi_arm_supers_timer(void);
 void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi);
+void bdi_lock_two(struct bdi_writeback *wb1, struct bdi_writeback *wb2);
 
 extern spinlock_t bdi_lock;
 extern struct list_head bdi_list;
--
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