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Subject[PATCH, RFC] ext4: Replace hackish ext4_mb_poll_new_transaction with commit callback
Date
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>
---
fs/ext4/ext4_sb.h | 3 --
fs/ext4/mballoc.c | 85 +++++++++----------------------------------------
fs/ext4/mballoc.h | 3 +-
fs/jbd2/commit.c | 3 ++
fs/jbd2/transaction.c | 1 +
include/linux/jbd2.h | 9 +++++
6 files changed, 29 insertions(+), 75 deletions(-)

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 6a0b40d..445fde6 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 da1da1f..dfe17a1 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 94cb7b9..b5dff1f 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 0abe02c..8b119e1 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 e5d5405..39b7805 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 d2e91ea..3018583 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
*/
--
1.5.6.1.205.ge2c7.dirty


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