writeback: move dirty inodes from super_block to backing_dev_info

This is a first step at introducing per-bdi flusher threads. We should
have no change in behaviour, although sb_has_dirty_inodes() is now
ridiculously expensive, as there's no easy way to answer that question.
Not a huge problem, since it'll be deleted in subsequent patches.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

6 files changed, 165 insertions, 84 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 271e5f44e871..45ad4bb700e6 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -25,6 +25,7 @@
 #include <linux/buffer_head.h>
 #include "internal.h"
 
+#define inode_to_bdi(inode)     ((inode)->i_mapping->backing_dev_info)
 
 /**
  * writeback_acquire - attempt to get exclusive writeback access to a device
@@ -165,12 +166,13 @@ void __mark_inode_dirty(struct inode *inode, int flags)
                         goto out;
 
                 /*
-                 * If the inode was already on s_dirty/s_io/s_more_io, don't
-                 * reposition it (that would break s_dirty time-ordering).
+                 * 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) {
                         inode->dirtied_when = jiffies;
-                        list_move(&inode->i_list, &sb->s_dirty);
+                        list_move(&inode->i_list,
+                                        &inode_to_bdi(inode)->b_dirty);
                 }
         }
 out:
@@ -191,31 +193,30 @@ static int write_inode(struct inode *inode, int sync)
  * furthest end of its superblock's dirty-inode list.
  *
  * Before stamping the inode's ->dirtied_when, we check to see whether it is
- * already the most-recently-dirtied inode on the s_dirty list.  If that is
+ * already the most-recently-dirtied inode on the b_dirty list.  If that is
  * 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)
 {
-        struct super_block *sb = inode->i_sb;
+        struct backing_dev_info *bdi = inode_to_bdi(inode);
 
-        if (!list_empty(&sb->s_dirty)) {
-                struct inode *tail_inode;
+        if (!list_empty(&bdi->b_dirty)) {
+                struct inode *tail;
 
-                tail_inode = list_entry(sb->s_dirty.next, struct inode, i_list);
-                if (time_before(inode->dirtied_when,
-                                tail_inode->dirtied_when))
+                tail = list_entry(bdi->b_dirty.next, struct inode, i_list);
+                if (time_before(inode->dirtied_when, tail->dirtied_when))
                         inode->dirtied_when = jiffies;
         }
-        list_move(&inode->i_list, &sb->s_dirty);
+        list_move(&inode->i_list, &bdi->b_dirty);
 }
 
 /*
- * requeue inode for re-scanning after sb->s_io list is exhausted.
+ * requeue inode for re-scanning after bdi->b_io list is exhausted.
  */
 static void requeue_io(struct inode *inode)
 {
-        list_move(&inode->i_list, &inode->i_sb->s_more_io);
+        list_move(&inode->i_list, &inode_to_bdi(inode)->b_more_io);
 }
 
 static void inode_sync_complete(struct inode *inode)
@@ -262,18 +263,50 @@ static void move_expired_inodes(struct list_head *delaying_queue,
 /*
  * Queue all expired dirty inodes for io, eldest first.
  */
-static void queue_io(struct super_block *sb,
-                                unsigned long *older_than_this)
+static void queue_io(struct backing_dev_info *bdi,
+                     unsigned long *older_than_this)
+{
+        list_splice_init(&bdi->b_more_io, bdi->b_io.prev);
+        move_expired_inodes(&bdi->b_dirty, &bdi->b_io, older_than_this);
+}
+
+static int sb_on_inode_list(struct super_block *sb, struct list_head *list)
 {
-        list_splice_init(&sb->s_more_io, sb->s_io.prev);
-        move_expired_inodes(&sb->s_dirty, &sb->s_io, older_than_this);
+        struct inode *inode;
+        int ret = 0;
+
+        spin_lock(&inode_lock);
+        list_for_each_entry(inode, list, i_list) {
+                if (inode->i_sb == sb) {
+                        ret = 1;
+                        break;
+                }
+        }
+        spin_unlock(&inode_lock);
+        return ret;
 }
 
 int sb_has_dirty_inodes(struct super_block *sb)
 {
-        return !list_empty(&sb->s_dirty) ||
-               !list_empty(&sb->s_io) ||
-               !list_empty(&sb->s_more_io);
+        struct backing_dev_info *bdi;
+        int ret = 0;
+
+        /*
+         * This is REALLY expensive right now, but it'll go away
+         * when the bdi writeback is introduced
+         */
+        mutex_lock(&bdi_lock);
+        list_for_each_entry(bdi, &bdi_list, bdi_list) {
+                if (sb_on_inode_list(sb, &bdi->b_dirty) ||
+                    sb_on_inode_list(sb, &bdi->b_io) ||
+                    sb_on_inode_list(sb, &bdi->b_more_io)) {
+                        ret = 1;
+                        break;
+                }
+        }
+        mutex_unlock(&bdi_lock);
+
+        return ret;
 }
 EXPORT_SYMBOL(sb_has_dirty_inodes);
 
@@ -322,11 +355,11 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         if (inode->i_state & I_SYNC) {
                 /*
                  * If this inode is locked for writeback and we are not doing
-                 * writeback-for-data-integrity, move it to s_more_io so that
+                 * writeback-for-data-integrity, move it to b_more_io so that
                  * writeback can proceed with the other inodes on s_io.
                  *
                  * We'll have another go at writing back this inode when we
-                 * completed a full scan of s_io.
+                 * completed a full scan of b_io.
                  */
                 if (!wait) {
                         requeue_io(inode);
@@ -371,11 +404,11 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                         /*
                          * We didn't write back all the pages.  nfs_writepages()
                          * sometimes bales out without doing anything. Redirty
-                         * the inode; Move it from s_io onto s_more_io/s_dirty.
+                         * the inode; Move it from b_io onto b_more_io/b_dirty.
                          */
                         /*
                          * akpm: if the caller was the kupdate function we put
-                         * this inode at the head of s_dirty so it gets first
+                         * this inode at the head of b_dirty so it gets first
                          * consideration.  Otherwise, move it to the tail, for
                          * the reasons described there.  I'm not really sure
                          * how much sense this makes.  Presumably I had a good
@@ -385,7 +418,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
                         if (wbc->for_kupdate) {
                                 /*
                                  * For the kupdate function we move the inode
-                                 * to s_more_io so it will get more writeout as
+                                 * to b_more_io so it will get more writeout as
                                  * soon as the queue becomes uncongested.
                                  */
                                 inode->i_state |= I_DIRTY_PAGES;
@@ -433,51 +466,34 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
         return ret;
 }
 
-/*
- * Write out a superblock's list of dirty inodes.  A wait will be performed
- * upon no inodes, all inodes or the final one, depending upon sync_mode.
- *
- * If older_than_this is non-NULL, then only write out inodes which
- * had their first dirtying at a time earlier than *older_than_this.
- *
- * If we're a pdflush thread, then implement pdflush collision avoidance
- * against the entire list.
- *
- * If `bdi' is non-zero then we're being asked to writeback a specific queue.
- * This function assumes that the blockdev superblock's inodes are backed by
- * a variety of queues, so all inodes are searched.  For other superblocks,
- * assume that all inodes are backed by the same queue.
- *
- * FIXME: this linear search could get expensive with many fileystems.  But
- * how to fix?  We need to go from an address_space to all inodes which share
- * a queue with that address_space.  (Easy: have a global "dirty superblocks"
- * list).
- *
- * The inodes to be written are parked on sb->s_io.  They are moved back onto
- * sb->s_dirty as they are selected for writing.  This way, none can be missed
- * on the writer throttling path, and we get decent balancing between many
- * throttled threads: we don't want them all piling up on inode_sync_wait.
- */
-static void generic_sync_sb_inodes(struct super_block *sb,
-                                   struct writeback_control *wbc)
+static void generic_sync_bdi_inodes(struct backing_dev_info *bdi,
+                                    struct writeback_control *wbc,
+                                    struct super_block *sb)
 {
+        const int is_blkdev_sb = sb_is_blkdev_sb(sb);
         const unsigned long start = jiffies;    /* livelock avoidance */
-        int sync = wbc->sync_mode == WB_SYNC_ALL;
 
         spin_lock(&inode_lock);
-        if (!wbc->for_kupdate || list_empty(&sb->s_io))
-                queue_io(sb, wbc->older_than_this);
 
-        while (!list_empty(&sb->s_io)) {
-                struct inode *inode = list_entry(sb->s_io.prev,
+        if (!wbc->for_kupdate || list_empty(&bdi->b_io))
+                queue_io(bdi, wbc->older_than_this);
+
+        while (!list_empty(&bdi->b_io)) {
+                struct inode *inode = list_entry(bdi->b_io.prev,
                                                 struct inode, i_list);
-                struct address_space *mapping = inode->i_mapping;
-                struct backing_dev_info *bdi = mapping->backing_dev_info;
                 long pages_skipped;
 
+                /*
+                 * super block given and doesn't match, skip this inode
+                 */
+                if (sb && sb != inode->i_sb) {
+                        redirty_tail(inode);
+                        continue;
+                }
+
                 if (!bdi_cap_writeback_dirty(bdi)) {
                         redirty_tail(inode);
-                        if (sb_is_blkdev_sb(sb)) {
+                        if (is_blkdev_sb) {
                                 /*
                                  * Dirty memory-backed blockdev: the ramdisk
                                  * driver does this.  Skip just this inode
@@ -499,14 +515,14 @@ static void generic_sync_sb_inodes(struct super_block *sb,
 
                 if (wbc->nonblocking && bdi_write_congested(bdi)) {
                         wbc->encountered_congestion = 1;
-                        if (!sb_is_blkdev_sb(sb))
+                        if (!is_blkdev_sb)
                                 break;          /* Skip a congested fs */
                         requeue_io(inode);
                         continue;               /* Skip a congested blockdev */
                 }
 
                 if (wbc->bdi && bdi != wbc->bdi) {
-                        if (!sb_is_blkdev_sb(sb))
+                        if (!is_blkdev_sb)
                                 break;          /* fs has the wrong queue */
                         requeue_io(inode);
                         continue;               /* blockdev has wrong queue */
@@ -544,13 +560,57 @@ static void generic_sync_sb_inodes(struct super_block *sb,
                         wbc->more_io = 1;
                         break;
                 }
-                if (!list_empty(&sb->s_more_io))
+                if (!list_empty(&bdi->b_more_io))
                         wbc->more_io = 1;
         }
 
-        if (sync) {
+        spin_unlock(&inode_lock);
+        /* Leave any unwritten inodes on b_io */
+}
+
+/*
+ * Write out a superblock's list of dirty inodes.  A wait will be performed
+ * upon no inodes, all inodes or the final one, depending upon sync_mode.
+ *
+ * If older_than_this is non-NULL, then only write out inodes which
+ * had their first dirtying at a time earlier than *older_than_this.
+ *
+ * If we're a pdlfush thread, then implement pdflush collision avoidance
+ * against the entire list.
+ *
+ * If `bdi' is non-zero then we're being asked to writeback a specific queue.
+ * This function assumes that the blockdev superblock's inodes are backed by
+ * a variety of queues, so all inodes are searched.  For other superblocks,
+ * assume that all inodes are backed by the same queue.
+ *
+ * FIXME: this linear search could get expensive with many fileystems.  But
+ * how to fix?  We need to go from an address_space to all inodes which share
+ * a queue with that address_space.  (Easy: have a global "dirty superblocks"
+ * list).
+ *
+ * The inodes to be written are parked on bdi->b_io.  They are moved back onto
+ * bdi->b_dirty as they are selected for writing.  This way, none can be missed
+ * on the writer throttling path, and we get decent balancing between many
+ * throttled threads: we don't want them all piling up on inode_sync_wait.
+ */
+static void generic_sync_sb_inodes(struct super_block *sb,
+                                   struct writeback_control *wbc)
+{
+        struct backing_dev_info *bdi;
+
+        if (!wbc->bdi) {
+                mutex_lock(&bdi_lock);
+                list_for_each_entry(bdi, &bdi_list, bdi_list)
+                        generic_sync_bdi_inodes(bdi, wbc, sb);
+                mutex_unlock(&bdi_lock);
+        } else
+                generic_sync_bdi_inodes(wbc->bdi, wbc, sb);
+
+        if (wbc->sync_mode == WB_SYNC_ALL) {
                 struct inode *inode, *old_inode = NULL;
 
+                spin_lock(&inode_lock);
+
                 /*
                  * Data integrity sync. Must wait for all pages under writeback,
                  * because there may have been pages dirtied before our sync
@@ -588,10 +648,7 @@ static void generic_sync_sb_inodes(struct super_block *sb,
                 }
                 spin_unlock(&inode_lock);
                 iput(old_inode);
-        } else
-                spin_unlock(&inode_lock);
-
-        return;         /* Leave any unwritten inodes on s_io */
+        }
 }
 
 /*
@@ -599,8 +656,8 @@ static void generic_sync_sb_inodes(struct super_block *sb,
  *
  * Note:
  * We don't need to grab a reference to superblock here. If it has non-empty
- * ->s_dirty it's hadn't been killed yet and kill_super() won't proceed
- * past sync_inodes_sb() until the ->s_dirty/s_io/s_more_io lists are all
+ * ->b_dirty it's hadn't been killed yet and kill_super() won't proceed
+ * past sync_inodes_sb() until the ->b_dirty/b_io/b_more_io lists are all
  * empty. Since __sync_single_inode() regains inode_lock before it finally moves
  * inode from superblock lists we are OK.
  *
diff --git a/fs/super.c b/fs/super.c
index 2761d3e22ed9..0d22ce3be4aa 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -62,9 +62,6 @@ static struct super_block *alloc_super(struct file_system_type *type)
                         s = NULL;
                         goto out;
                 }
-                INIT_LIST_HEAD(&s->s_dirty);
-                INIT_LIST_HEAD(&s->s_io);
-                INIT_LIST_HEAD(&s->s_more_io);
                 INIT_LIST_HEAD(&s->s_files);
                 INIT_LIST_HEAD(&s->s_instances);
                 INIT_HLIST_HEAD(&s->s_anon);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 1d52425a6118..928cd5484f4d 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -40,6 +40,8 @@ enum bdi_stat_item {
 #define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
 
 struct backing_dev_info {
+        struct list_head bdi_list;
+
         unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
         unsigned long state;    /* Always use atomic bitops on this */
         unsigned int capabilities; /* Device capabilities */
@@ -58,6 +60,10 @@ struct backing_dev_info {
 
         struct device *dev;
 
+        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 */
+
 #ifdef CONFIG_DEBUG_FS
         struct dentry *debug_dir;
         struct dentry *debug_stats;
@@ -72,6 +78,9 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
 int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev);
 void bdi_unregister(struct backing_dev_info *bdi);
 
+extern struct mutex bdi_lock;
+extern struct list_head bdi_list;
+
 static inline void __add_bdi_stat(struct backing_dev_info *bdi,
                 enum bdi_stat_item item, s64 amount)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 46ff7dd6e164..56371be1be65 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -715,7 +715,7 @@ struct posix_acl;
 
 struct inode {
         struct hlist_node       i_hash;
-        struct list_head        i_list;
+        struct list_head        i_list;         /* backing dev IO list */
         struct list_head        i_sb_list;
         struct list_head        i_dentry;
         unsigned long           i_ino;
@@ -1336,9 +1336,6 @@ struct super_block {
         struct xattr_handler    **s_xattr;
 
         struct list_head        s_inodes;       /* all inodes */
-        struct list_head        s_dirty;        /* dirty inodes */
-        struct list_head        s_io;           /* parked for writeback */
-        struct list_head        s_more_io;      /* parked for more writeback */
         struct hlist_head       s_anon;         /* anonymous dentries for (nfs) exporting */
         struct list_head        s_files;
         /* s_dentry_lru and s_nr_dentry_unused are protected by dcache_lock */
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c86edd244294..6f163e0f0509 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -22,6 +22,8 @@ struct backing_dev_info default_backing_dev_info = {
 EXPORT_SYMBOL_GPL(default_backing_dev_info);
 
 static struct class *bdi_class;
+DEFINE_MUTEX(bdi_lock);
+LIST_HEAD(bdi_list);
 
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
@@ -211,6 +213,10 @@ int bdi_register(struct backing_dev_info *bdi, struct device *parent,
                 goto exit;
         }
 
+        mutex_lock(&bdi_lock);
+        list_add_tail(&bdi->bdi_list, &bdi_list);
+        mutex_unlock(&bdi_lock);
+
         bdi->dev = dev;
         bdi_debug_register(bdi, dev_name(dev));
 
@@ -225,9 +231,17 @@ int bdi_register_dev(struct backing_dev_info *bdi, dev_t dev)
 }
 EXPORT_SYMBOL(bdi_register_dev);
 
+static void bdi_remove_from_list(struct backing_dev_info *bdi)
+{
+        mutex_lock(&bdi_lock);
+        list_del(&bdi->bdi_list);
+        mutex_unlock(&bdi_lock);
+}
+
 void bdi_unregister(struct backing_dev_info *bdi)
 {
         if (bdi->dev) {
+                bdi_remove_from_list(bdi);
                 bdi_debug_unregister(bdi);
                 device_unregister(bdi->dev);
                 bdi->dev = NULL;
@@ -245,6 +259,10 @@ int bdi_init(struct backing_dev_info *bdi)
         bdi->min_ratio = 0;
         bdi->max_ratio = 100;
         bdi->max_prop_frac = PROP_FRAC_BASE;
+        INIT_LIST_HEAD(&bdi->bdi_list);
+        INIT_LIST_HEAD(&bdi->b_io);
+        INIT_LIST_HEAD(&bdi->b_dirty);
+        INIT_LIST_HEAD(&bdi->b_more_io);
 
         for (i = 0; i < NR_BDI_STAT_ITEMS; i++) {
                 err = percpu_counter_init(&bdi->bdi_stat[i], 0);
@@ -259,6 +277,8 @@ int bdi_init(struct backing_dev_info *bdi)
 err:
                 while (i--)
                         percpu_counter_destroy(&bdi->bdi_stat[i]);
+
+                bdi_remove_from_list(bdi);
         }
 
         return err;
@@ -269,6 +289,10 @@ void bdi_destroy(struct backing_dev_info *bdi)
 {
         int i;
 
+        WARN_ON(!list_empty(&bdi->b_dirty));
+        WARN_ON(!list_empty(&bdi->b_io));
+        WARN_ON(!list_empty(&bdi->b_more_io));
+
         bdi_unregister(bdi);
 
         for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 81627ebcd313..f8341b6019bf 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -320,15 +320,13 @@ static void task_dirty_limit(struct task_struct *tsk, unsigned long *pdirty)
 /*
  *
  */
-static DEFINE_SPINLOCK(bdi_lock);
 static unsigned int bdi_min_ratio;
 
 int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
 {
         int ret = 0;
-        unsigned long flags;
 
-        spin_lock_irqsave(&bdi_lock, flags);
+        mutex_lock(&bdi_lock);
         if (min_ratio > bdi->max_ratio) {
                 ret = -EINVAL;
         } else {
@@ -340,27 +338,26 @@ int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio)
                         ret = -EINVAL;
                 }
         }
-        spin_unlock_irqrestore(&bdi_lock, flags);
+        mutex_unlock(&bdi_lock);
 
         return ret;
 }
 
 int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned max_ratio)
 {
-        unsigned long flags;
         int ret = 0;
 
         if (max_ratio > 100)
                 return -EINVAL;
 
-        spin_lock_irqsave(&bdi_lock, flags);
+        mutex_lock(&bdi_lock);
         if (bdi->min_ratio > max_ratio) {
                 ret = -EINVAL;
         } else {
                 bdi->max_ratio = max_ratio;
                 bdi->max_prop_frac = (PROP_FRAC_BASE * max_ratio) / 100;
         }
-        spin_unlock_irqrestore(&bdi_lock, flags);
+        mutex_unlock(&bdi_lock);
 
         return ret;
 }