ext4: Replace hackish ext4_mb_poll_new_transaction with commit callback

The multiblock allocator needs to be able to release blocks (and issue
a blkdev discard request) when the transaction which freed those
blocks is committed.  Previously this was done via a polling mechanism
when blocks are allocated or freed.  A much better way of doing things
is to create a jbd2 callback function and attaching the list of blocks
to be freed directly to the transaction structure.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

6 files changed, 29 insertions, 75 deletions

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 6a0b40d43264..445fde603df8 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -99,9 +99,6 @@ struct ext4_sb_info {
         struct inode *s_buddy_cache;
         long s_blocks_reserved;
         spinlock_t s_reserve_lock;
-        struct list_head s_active_transaction;
-        struct list_head s_closed_transaction;
-        struct list_head s_committed_transaction;
         spinlock_t s_md_lock;
         tid_t s_last_transaction;
         unsigned short *s_mb_offsets, *s_mb_maxs;
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index da1da1fe2b14..dfe17a134052 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2523,9 +2523,6 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
         }
 
         spin_lock_init(&sbi->s_md_lock);
-        INIT_LIST_HEAD(&sbi->s_active_transaction);
-        INIT_LIST_HEAD(&sbi->s_closed_transaction);
-        INIT_LIST_HEAD(&sbi->s_committed_transaction);
         spin_lock_init(&sbi->s_bal_lock);
 
         sbi->s_mb_max_to_scan = MB_DEFAULT_MAX_TO_SCAN;
@@ -2554,6 +2551,8 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
         ext4_mb_init_per_dev_proc(sb);
         ext4_mb_history_init(sb);
 
+        sbi->s_journal->j_commit_callback = release_blocks_on_commit;
+
         printk(KERN_INFO "EXT4-fs: mballoc enabled\n");
         return 0;
 }
@@ -2583,15 +2582,6 @@ int ext4_mb_release(struct super_block *sb)
         struct ext4_group_info *grinfo;
         struct ext4_sb_info *sbi = EXT4_SB(sb);
 
-        /* release freed, non-committed blocks */
-        spin_lock(&sbi->s_md_lock);
-        list_splice_init(&sbi->s_closed_transaction,
-                        &sbi->s_committed_transaction);
-        list_splice_init(&sbi->s_active_transaction,
-                        &sbi->s_committed_transaction);
-        spin_unlock(&sbi->s_md_lock);
-        ext4_mb_free_committed_blocks(sb);
-
         if (sbi->s_group_info) {
                 for (i = 0; i < sbi->s_groups_count; i++) {
                         grinfo = ext4_get_group_info(sb, i);
@@ -2645,36 +2635,25 @@ int ext4_mb_release(struct super_block *sb)
         return 0;
 }
 
-static noinline_for_stack void
-ext4_mb_free_committed_blocks(struct super_block *sb)
+/*
+ * This function is called by the jbd2 layer once the commit has finished,
+ * so we know we can free the blocks that were released with that commit.
+ */
+static void release_blocks_on_commit(journal_t *journal, transaction_t *txn)
 {
+        struct super_block *sb = journal->j_private;
         struct ext4_buddy e4b;
         struct ext4_group_info *db;
-        struct ext4_sb_info *sbi = EXT4_SB(sb);
         int err, count = 0, count2 = 0;
         struct ext4_free_data *entry;
         ext4_fsblk_t discard_block;
+        struct list_head *l, *ltmp;
 
-        if (list_empty(&sbi->s_committed_transaction))
-                return;
-
-        /* there is committed blocks to be freed yet */
-        do {
-                /* get next array of blocks */
-                entry = NULL;
-                spin_lock(&sbi->s_md_lock);
-                if (!list_empty(&sbi->s_committed_transaction)) {
-                        entry = list_entry(sbi->s_committed_transaction.next,
-                                        struct ext4_free_data, list);
-                        list_del(&entry->list);
-                }
-                spin_unlock(&sbi->s_md_lock);
-
-                if (entry == NULL)
-                        break;
+        list_for_each_safe(l, ltmp, &txn->t_private_list) {
+                entry = list_entry(l, struct ext4_free_data, list);
 
                 mb_debug("gonna free %u blocks in group %lu (0x%p):",
-                                entry->count, entry->group, entry);
+                         entry->count, entry->group, entry);
 
                 err = ext4_mb_load_buddy(sb, entry->group, &e4b);
                 /* we expect to find existing buddy because it's pinned */
@@ -2706,7 +2685,7 @@ ext4_mb_free_committed_blocks(struct super_block *sb)
 
                 kmem_cache_free(ext4_free_ext_cachep, entry);
                 ext4_mb_release_desc(&e4b);
-        } while (1);
+        }
 
         mb_debug("freed %u blocks in %u structures\n", count, count2);
 }
@@ -4348,8 +4327,6 @@ ext4_fsblk_t ext4_mb_new_blocks(handle_t *handle,
                 goto out1;
         }
 
-        ext4_mb_poll_new_transaction(sb, handle);
-
         *errp = ext4_mb_initialize_context(ac, ar);
         if (*errp) {
                 ar->len = 0;
@@ -4408,36 +4385,6 @@ out1:
 
         return block;
 }
-static void ext4_mb_poll_new_transaction(struct super_block *sb,
-                                                handle_t *handle)
-{
-        struct ext4_sb_info *sbi = EXT4_SB(sb);
-
-        if (sbi->s_last_transaction == handle->h_transaction->t_tid)
-                return;
-
-        /* new transaction! time to close last one and free blocks for
-         * committed transaction. we know that only transaction can be
-         * active, so previos transaction can be being logged and we
-         * know that transaction before previous is known to be already
-         * logged. this means that now we may free blocks freed in all
-         * transactions before previous one. hope I'm clear enough ... */
-
-        spin_lock(&sbi->s_md_lock);
-        if (sbi->s_last_transaction != handle->h_transaction->t_tid) {
-                mb_debug("new transaction %lu, old %lu\n",
-                                (unsigned long) handle->h_transaction->t_tid,
-                                (unsigned long) sbi->s_last_transaction);
-                list_splice_init(&sbi->s_closed_transaction,
-                                &sbi->s_committed_transaction);
-                list_splice_init(&sbi->s_active_transaction,
-                                &sbi->s_closed_transaction);
-                sbi->s_last_transaction = handle->h_transaction->t_tid;
-        }
-        spin_unlock(&sbi->s_md_lock);
-
-        ext4_mb_free_committed_blocks(sb);
-}
 
 /*
  * We can merge two free data extents only if the physical blocks
@@ -4531,9 +4478,9 @@ ext4_mb_free_metadata(handle_t *handle, struct ext4_buddy *e4b,
                         kmem_cache_free(ext4_free_ext_cachep, entry);
                 }
         }
-        /* Add the extent to active_transaction list */
+        /* Add the extent to transaction's private list */
         spin_lock(&sbi->s_md_lock);
-        list_add(&new_entry->list, &sbi->s_active_transaction);
+        list_add(&new_entry->list, &handle->h_transaction->t_private_list);
         spin_unlock(&sbi->s_md_lock);
         ext4_unlock_group(sb, group);
         return 0;
@@ -4562,8 +4509,6 @@ void ext4_mb_free_blocks(handle_t *handle, struct inode *inode,
 
         *freed = 0;
 
-        ext4_mb_poll_new_transaction(sb, handle);
-
         sbi = EXT4_SB(sb);
         es = EXT4_SB(sb)->s_es;
         if (block < le32_to_cpu(es->s_first_data_block) ||
diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
index 94cb7b9fe3ee..b5dff1fff1e5 100644
--- a/fs/ext4/mballoc.h
+++ b/fs/ext4/mballoc.h
@@ -269,8 +269,6 @@ struct buffer_head *read_block_bitmap(struct super_block *, ext4_group_t);
 
 static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                         ext4_group_t group);
-static void ext4_mb_poll_new_transaction(struct super_block *, handle_t *);
-static void ext4_mb_free_committed_blocks(struct super_block *);
 static void ext4_mb_return_to_preallocation(struct inode *inode,
                                         struct ext4_buddy *e4b, sector_t block,
                                         int count);
@@ -278,6 +276,7 @@ static void ext4_mb_put_pa(struct ext4_allocation_context *,
                         struct super_block *, struct ext4_prealloc_space *pa);
 static int ext4_mb_init_per_dev_proc(struct super_block *sb);
 static int ext4_mb_destroy_per_dev_proc(struct super_block *sb);
+static void release_blocks_on_commit(journal_t *journal, transaction_t *txn);
 
 
 static inline void ext4_lock_group(struct super_block *sb, ext4_group_t group)
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 0abe02c4242a..8b119e16aa36 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -995,6 +995,9 @@ restart_loop:
         }
         spin_unlock(&journal->j_list_lock);
 
+        if (journal->j_commit_callback)
+                journal->j_commit_callback(journal, commit_transaction);
+
         trace_mark(jbd2_end_commit, "dev %s transaction %d head %d",
                    journal->j_devname, commit_transaction->t_tid,
                    journal->j_tail_sequence);
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index e5d540588fa9..39b7805a599a 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -52,6 +52,7 @@ jbd2_get_transaction(journal_t *journal, transaction_t *transaction)
         transaction->t_expires = jiffies + journal->j_commit_interval;
         spin_lock_init(&transaction->t_handle_lock);
         INIT_LIST_HEAD(&transaction->t_inode_list);
+        INIT_LIST_HEAD(&transaction->t_private_list);
 
         /* Set up the commit timer for the new transaction. */
         journal->j_commit_timer.expires = round_jiffies(transaction->t_expires);
diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
index 463d6f10b64f..c7d106ef22e2 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -641,6 +641,11 @@ struct transaction_s
          */
         int t_handle_count;
 
+        /*
+         * For use by the filesystem to store fs-specific data
+         * structures associated with the transaction
+         */
+        struct list_head        t_private_list;
 };
 
 struct transaction_run_stats_s {
@@ -935,6 +940,10 @@ struct journal_s
 
         pid_t                   j_last_sync_writer;
 
+        /* This function is called when a transaction is closed */
+        void                    (*j_commit_callback)(journal_t *,
+                                                     transaction_t *);
+
         /*
          * Journal statistics
          */