jbd: Refine commit writeout logic
Jan Kara [Mon, 21 Feb 2011 16:25:37 +0000 (17:25 +0100)]
Currently we write out all journal buffers in WRITE_SYNC mode. This improves
performance for fsync heavy workloads but hinders performance when writes
are mostly asynchronous, most noticably it slows down readers and users
complain about slow desktop response etc.

So submit writes as asynchronous in the normal case and only submit writes as
WRITE_SYNC if we detect someone is waiting for current transaction commit.

I've gathered some numbers to back this change. The first is the read latency
test. It measures time to read 1 MB after several seconds of sleeping in
presence of streaming writes.

Top 10 times (out of 90) in us:
Before After
2131586 697473
1709932 557487
1564598 535642
1480462 347573
1478579 323153
1408496 222181
1388960 181273
1329565 181070
1252486 172832
1223265 172278

Average:
619377 82180

So the improvement in both maximum and average latency is massive.

I've measured fsync throughput by:
fs_mark -n 100 -t 1 -s 16384 -d /mnt/fsync/ -S 1 -L 4

in presence of streaming reader. The numbers (fsyncs/s) are:
Before After
9.9 6.3
6.8 6.0
6.3 6.2
5.8 6.1

So fsync performance seems unharmed by this change.

Signed-off-by: Jan Kara <jack@suse.cz>

fs/jbd/commit.c
fs/jbd/journal.c
fs/jbd/transaction.c
include/linux/jbd.h
include/trace/events/jbd.h

index f2b9a57..9d31e6a 100644 (file)
@@ -298,6 +298,7 @@ void journal_commit_transaction(journal_t *journal)
        int tag_flag;
        int i;
        struct blk_plug plug;
+       int write_op = WRITE;
 
        /*
         * First job: lock down the current transaction and wait for
@@ -413,13 +414,16 @@ void journal_commit_transaction(journal_t *journal)
 
        jbd_debug (3, "JBD: commit phase 2\n");
 
+       if (tid_geq(journal->j_commit_waited, commit_transaction->t_tid))
+               write_op = WRITE_SYNC;
+
        /*
         * Now start flushing things to disk, in the order they appear
         * on the transaction lists.  Data blocks go first.
         */
        blk_start_plug(&plug);
        err = journal_submit_data_buffers(journal, commit_transaction,
-                                         WRITE_SYNC);
+                                         write_op);
        blk_finish_plug(&plug);
 
        /*
@@ -478,7 +482,7 @@ void journal_commit_transaction(journal_t *journal)
 
        blk_start_plug(&plug);
 
-       journal_write_revoke_records(journal, commit_transaction, WRITE_SYNC);
+       journal_write_revoke_records(journal, commit_transaction, write_op);
 
        /*
         * If we found any dirty or locked buffers, then we should have
@@ -649,7 +653,7 @@ start_journal_io:
                                clear_buffer_dirty(bh);
                                set_buffer_uptodate(bh);
                                bh->b_end_io = journal_end_buffer_io_sync;
-                               submit_bh(WRITE_SYNC, bh);
+                               submit_bh(write_op, bh);
                        }
                        cond_resched();
 
index 0971e92..2047fd7 100644 (file)
@@ -563,6 +563,8 @@ int log_wait_commit(journal_t *journal, tid_t tid)
        spin_unlock(&journal->j_state_lock);
 #endif
        spin_lock(&journal->j_state_lock);
+       if (!tid_geq(journal->j_commit_waited, tid))
+               journal->j_commit_waited = tid;
        while (tid_gt(tid, journal->j_commit_sequence)) {
                jbd_debug(1, "JBD: want %d, j_commit_sequence=%d\n",
                                  tid, journal->j_commit_sequence);
index b2a7e52..febc10d 100644 (file)
@@ -1433,8 +1433,6 @@ int journal_stop(handle_t *handle)
                }
        }
 
-       if (handle->h_sync)
-               transaction->t_synchronous_commit = 1;
        current->journal_info = NULL;
        spin_lock(&journal->j_state_lock);
        spin_lock(&transaction->t_handle_lock);
index d211732..f265682 100644 (file)
@@ -479,12 +479,6 @@ struct transaction_s
         * How many handles used this transaction? [t_handle_lock]
         */
        int t_handle_count;
-
-       /*
-        * This transaction is being forced and some process is
-        * waiting for it to finish.
-        */
-       unsigned int t_synchronous_commit:1;
 };
 
 /**
@@ -531,6 +525,8 @@ struct transaction_s
  *  transaction
  * @j_commit_request: Sequence number of the most recent transaction wanting
  *     commit
+ * @j_commit_waited: Sequence number of the most recent transaction someone
+ *     is waiting for to commit.
  * @j_uuid: Uuid of client object.
  * @j_task: Pointer to the current commit thread for this journal
  * @j_max_transaction_buffers:  Maximum number of metadata buffers to allow in a
@@ -696,6 +692,13 @@ struct journal_s
        tid_t                   j_commit_request;
 
        /*
+        * Sequence number of the most recent transaction someone is waiting
+        * for to commit.
+        * [j_state_lock]
+        */
+       tid_t                   j_commit_waited;
+
+       /*
         * Journal uuid: identifies the object (filesystem, LVM volume etc)
         * backed by this journal.  This will eventually be replaced by an array
         * of uuids, allowing us to index multiple devices within a single
index aff64d8..9305e1b 100644 (file)
@@ -36,19 +36,17 @@ DECLARE_EVENT_CLASS(jbd_commit,
 
        TP_STRUCT__entry(
                __field(        dev_t,  dev                     )
-               __field(        char,   sync_commit             )
                __field(        int,    transaction             )
        ),
 
        TP_fast_assign(
                __entry->dev            = journal->j_fs_dev->bd_dev;
-               __entry->sync_commit = commit_transaction->t_synchronous_commit;
                __entry->transaction    = commit_transaction->t_tid;
        ),
 
-       TP_printk("dev %d,%d transaction %d sync %d",
+       TP_printk("dev %d,%d transaction %d",
                  MAJOR(__entry->dev), MINOR(__entry->dev),
-                 __entry->transaction, __entry->sync_commit)
+                 __entry->transaction)
 );
 
 DEFINE_EVENT(jbd_commit, jbd_start_commit,
@@ -87,19 +85,17 @@ TRACE_EVENT(jbd_drop_transaction,
 
        TP_STRUCT__entry(
                __field(        dev_t,  dev                     )
-               __field(        char,   sync_commit             )
                __field(        int,    transaction             )
        ),
 
        TP_fast_assign(
                __entry->dev            = journal->j_fs_dev->bd_dev;
-               __entry->sync_commit = commit_transaction->t_synchronous_commit;
                __entry->transaction    = commit_transaction->t_tid;
        ),
 
-       TP_printk("dev %d,%d transaction %d sync %d",
+       TP_printk("dev %d,%d transaction %d",
                  MAJOR(__entry->dev), MINOR(__entry->dev),
-                 __entry->transaction, __entry->sync_commit)
+                 __entry->transaction)
 );
 
 TRACE_EVENT(jbd_end_commit,
@@ -109,21 +105,19 @@ TRACE_EVENT(jbd_end_commit,
 
        TP_STRUCT__entry(
                __field(        dev_t,  dev                     )
-               __field(        char,   sync_commit             )
                __field(        int,    transaction             )
                __field(        int,    head                    )
        ),
 
        TP_fast_assign(
                __entry->dev            = journal->j_fs_dev->bd_dev;
-               __entry->sync_commit = commit_transaction->t_synchronous_commit;
                __entry->transaction    = commit_transaction->t_tid;
                __entry->head           = journal->j_tail_sequence;
        ),
 
-       TP_printk("dev %d,%d transaction %d sync %d head %d",
+       TP_printk("dev %d,%d transaction %d head %d",
                  MAJOR(__entry->dev), MINOR(__entry->dev),
-                 __entry->transaction, __entry->sync_commit, __entry->head)
+                 __entry->transaction, __entry->head)
 );
 
 TRACE_EVENT(jbd_do_submit_data,
@@ -133,19 +127,17 @@ TRACE_EVENT(jbd_do_submit_data,
 
        TP_STRUCT__entry(
                __field(        dev_t,  dev                     )
-               __field(        char,   sync_commit             )
                __field(        int,    transaction             )
        ),
 
        TP_fast_assign(
                __entry->dev            = journal->j_fs_dev->bd_dev;
-               __entry->sync_commit = commit_transaction->t_synchronous_commit;
                __entry->transaction    = commit_transaction->t_tid;
        ),
 
-       TP_printk("dev %d,%d transaction %d sync %d",
+       TP_printk("dev %d,%d transaction %d",
                  MAJOR(__entry->dev), MINOR(__entry->dev),
-                  __entry->transaction, __entry->sync_commit)
+                  __entry->transaction)
 );
 
 TRACE_EVENT(jbd_cleanup_journal_tail,