writeback: split inode_wb_list_lock into bdi_writeback.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.  It 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.

It reduces lock contentions to 1/4 in this test case:
10 HDD JBOD, 100 dd on each disk, XFS, 6GB ram

lock_stat version 0.3
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                              class name    con-bounces    contentions   waittime-min   waittime-max waittime-total    acq-bounces   acquisitions   holdtime-min   holdtime-max holdtime-total
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
vanilla 2.6.39-rc3:
                      inode_wb_list_lock:         42590          44433           0.12         147.74      144127.35         252274         886792           0.08         121.34      917211.23
                      ------------------
                      inode_wb_list_lock              2          [<ffffffff81165da5>] bdev_inode_switch_bdi+0x29/0x85
                      inode_wb_list_lock             34          [<ffffffff8115bd0b>] inode_wb_list_del+0x22/0x49
                      inode_wb_list_lock          12893          [<ffffffff8115bb53>] __mark_inode_dirty+0x170/0x1d0
                      inode_wb_list_lock          10702          [<ffffffff8115afef>] writeback_single_inode+0x16d/0x20a
                      ------------------
                      inode_wb_list_lock              2          [<ffffffff81165da5>] bdev_inode_switch_bdi+0x29/0x85
                      inode_wb_list_lock             19          [<ffffffff8115bd0b>] inode_wb_list_del+0x22/0x49
                      inode_wb_list_lock           5550          [<ffffffff8115bb53>] __mark_inode_dirty+0x170/0x1d0
                      inode_wb_list_lock           8511          [<ffffffff8115b4ad>] writeback_sb_inodes+0x10f/0x157

2.6.39-rc3 + patch:
                &(&wb->list_lock)->rlock:         11383          11657           0.14         151.69       40429.51          90825         527918           0.11         145.90      556843.37
                ------------------------
                &(&wb->list_lock)->rlock             10          [<ffffffff8115b189>] inode_wb_list_del+0x5f/0x86
                &(&wb->list_lock)->rlock           1493          [<ffffffff8115b1ed>] writeback_inodes_wb+0x3d/0x150
                &(&wb->list_lock)->rlock           3652          [<ffffffff8115a8e9>] writeback_sb_inodes+0x123/0x16f
                &(&wb->list_lock)->rlock           1412          [<ffffffff8115a38e>] writeback_single_inode+0x17f/0x223
                ------------------------
                &(&wb->list_lock)->rlock              3          [<ffffffff8110b5af>] bdi_lock_two+0x46/0x4b
                &(&wb->list_lock)->rlock              6          [<ffffffff8115b189>] inode_wb_list_del+0x5f/0x86
                &(&wb->list_lock)->rlock           2061          [<ffffffff8115af97>] __mark_inode_dirty+0x173/0x1cf
                &(&wb->list_lock)->rlock           2629          [<ffffffff8115a8e9>] writeback_sb_inodes+0x123/0x16f

hughd@google.com: fix recursive lock when bdi_lock_two() is called with new the same as old
akpm@linux-foundation.org: cleanup bdev_inode_switch_bdi() comment

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

3 files changed, 61 insertions, 57 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1a2421f908f0..3c9a03e51b62 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -44,24 +44,28 @@ inline struct block_device *I_BDEV(struct inode *inode)
 {
         return &BDEV_I(inode)->bdev;
 }
-
 EXPORT_SYMBOL(I_BDEV);
 
 /*
- * move the inode from it's current bdi to the a new bdi. if the inode is dirty
- * we need to move it onto the dirty list of @dst so that the inode is always
- * on the right list.
+ * Move the inode from its current bdi to a new bdi. If the inode is dirty we
+ * need to move it onto the dirty list of @dst so that the inode is always on
+ * the right list.
  */
 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;
+
+        if (unlikely(dst == old))               /* deadlock avoidance */
+                return;
+        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)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 664acdb2e7ef..36a30917e0dc 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -181,12 +181,13 @@ void bdi_start_background_writeback(struct backing_dev_info *bdi)
  */
 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.
@@ -196,11 +197,9 @@ void inode_wb_list_del(struct inode *inode)
  * 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;
 
@@ -214,11 +213,9 @@ static void redirty_tail(struct inode *inode)
 /*
  * 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);
 }
 
@@ -226,7 +223,7 @@ static void inode_sync_complete(struct inode *inode)
 {
         /*
          * Prevent speculative execution through
-         * spin_unlock(&inode_wb_list_lock);
+         * spin_unlock(&wb->list_lock);
          */
 
         smp_mb();
@@ -302,7 +299,7 @@ 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);
+        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);
 }
@@ -317,7 +314,8 @@ static int write_inode(struct inode *inode, struct writeback_control *wbc)
 /*
  * 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;
@@ -325,15 +323,15 @@ 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_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.
  *
@@ -344,13 +342,14 @@ static void inode_wait_for_writeback(struct inode *inode)
  * 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))
@@ -368,14 +367,14 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                  * 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);
@@ -384,7 +383,7 @@ 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_wb_list_lock);
+        spin_unlock(&wb->list_lock);
 
         ret = do_writepages(mapping, wbc);
 
@@ -415,7 +414,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                         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)) {
@@ -438,7 +437,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                                 /*
                                  * slice used up: queue for next turn
                                  */
-                                requeue_io(inode);
+                                requeue_io(inode, wb);
                         } else {
                                 /*
                                  * Writeback blocked by something other than
@@ -447,7 +446,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                                  * 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) {
                         /*
@@ -456,7 +455,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                          * 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
@@ -521,7 +520,7 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                                  * superblock, move all inodes not belonging
                                  * to it back onto the dirty list.
                                  */
-                                redirty_tail(inode);
+                                redirty_tail(inode, wb);
                                 continue;
                         }
 
@@ -541,7 +540,7 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                 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;
                 }
 
@@ -557,19 +556,19 @@ static int writeback_sb_inodes(struct super_block *sb, struct bdi_writeback *wb,
                 __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;
@@ -588,7 +587,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
 
         if (!wbc->wb_start)
                 wbc->wb_start = jiffies; /* livelock avoidance */
-        spin_lock(&inode_wb_list_lock);
+        spin_lock(&wb->list_lock);
 
         if (list_empty(&wb->b_io))
                 queue_io(wb, wbc->older_than_this);
@@ -598,7 +597,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
                 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);
@@ -607,7 +606,7 @@ void writeback_inodes_wb(struct bdi_writeback *wb,
                 if (ret)
                         break;
         }
-        spin_unlock(&inode_wb_list_lock);
+        spin_unlock(&wb->list_lock);
         /* Leave any unwritten inodes on b_io */
 }
 
@@ -616,11 +615,11 @@ static void __writeback_inodes_sb(struct super_block *sb,
 {
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        spin_lock(&inode_wb_list_lock);
+        spin_lock(&wb->list_lock);
         if (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);
 }
 
 /*
@@ -762,15 +761,15 @@ static long wb_writeback(struct bdi_writeback *wb,
                  * 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;
@@ -1104,10 +1103,10 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                         }
 
                         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);
@@ -1309,6 +1308,7 @@ 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,
@@ -1321,11 +1321,11 @@ int write_inode_now(struct inode *inode, int sync)
                 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;
@@ -1345,13 +1345,14 @@ 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);
diff --git a/fs/inode.c b/fs/inode.c
index 0f7e88a7803f..4be128cbc754 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -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
@@ -68,7 +68,6 @@ 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